Update versions for Vagrant and VirtualBox.

Update version of Vagrant from 1.8.6 to 2.0.2.
Update version of VirtualBox from 5.1.8 to 5.2.6.

We needed to update Vagrant because older versions have networking
problems on modern Macs, resulting in weird `apt` errors when
provisioning.

Commit message and some text tweaked by tabbott.

Vagrantfile

@@ -10,7 +10,7 @@ end
 if Vagrant::VERSION == "1.8.7" then
     path = `which curl`
     if path.include?('/opt/vagrant/embedded/bin/curl') then
-        puts "In Vagrant 1.8.7, curl is broken. Please use Vagrant 1.8.6 "\
+        puts "In Vagrant 1.8.7, curl is broken. Please use Vagrant 2.0.2 "\
              "or run 'sudo rm -f /opt/vagrant/embedded/bin/curl' to fix the "\
              "issue before provisioning. See "\
              "https://github.com/mitchellh/vagrant/issues/7997 "\

docs/development/setup-vagrant.md

@@ -47,7 +47,7 @@ proxy](#specifying-a-proxy) if you need a proxy to access the internet.)
 
 - **All**: 2GB available RAM, Active broadband internet connection, [GitHub account][set-up-git].
 - **macOS**: macOS (10.11 El Capitan or 10.12 Sierra recommended),
-  Git, VirtualBox (version [5.1.8][vbox-dl-macos]
+  Git, VirtualBox (version [5.2.6][vbox-dl-macos]
   recommended -- we find it's more stable than more recent versions),
   [Vagrant][vagrant-dl-macos].
 - **Ubuntu**: 14.04 64-bit or 16.04 64-bit, Git, [Vagrant][vagrant-dl-deb], lxc.
@@ -82,8 +82,8 @@ Jump to:
 
 #### macOS
 
-1. Install [Vagrant][vagrant-dl-macos] (1.8.4-1.8.6, do not use 1.8.7).
+1. Install [Vagrant][vagrant-dl-macos] (2.0.2).
-2. Install [VirtualBox][vbox-dl-macos] (5.1.8).
+2. Install [VirtualBox][vbox-dl-macos] (5.2.6).
 
 (For a non-free option, but better performance, you can also use [VMWare
 Fusion][vmware-fusion-dl] with the [VMWare Fusion Vagrant
@@ -100,7 +100,7 @@ after which you can jump to [Step 2: Get Zulip Code](#step-2-get-zulip-code):
 
 ```
 sudo apt-get -y purge vagrant && \
-wget https://releases.hashicorp.com/vagrant/1.8.6/vagrant_1.8.6_x86_64.deb && \
+wget https://releases.hashicorp.com/vagrant/2.0.2/vagrant_2.0.2_x86_64.deb && \
 sudo dpkg -i vagrant*.deb && \
 sudo apt-get -y install build-essential git ruby lxc lxc-templates cgroup-lite redir && \
 vagrant plugin install vagrant-lxc && \
@@ -122,11 +122,11 @@ christie@ubuntu-desktop:~
 $ sudo apt-get purge vagrant
 ```
 
-Now download and install the .deb package for [Vagrant 1.8.6][vagrant-dl-deb]:
+Now download and install the .deb package for [Vagrant 2.0.2][vagrant-dl-deb]:
 
 ```
 christie@ubuntu-desktop:~
-$ wget https://releases.hashicorp.com/vagrant/1.8.6/vagrant_1.8.6_x86_64.deb
+$ wget https://releases.hashicorp.com/vagrant/2.0.2/vagrant_2.0.2_x86_64.deb
 
 christie@ubuntu-desktop:~
 $ sudo dpkg -i vagrant*.deb
@@ -187,7 +187,7 @@ paste the following into your terminal after which you can jump to
 
 ```
 sudo apt-get -y purge vagrant && \
-wget https://releases.hashicorp.com/vagrant/1.8.6/vagrant_1.8.6_x86_64.deb && \
+wget https://releases.hashicorp.com/vagrant/2.0.2/vagrant_2.0.2_x86_64.deb && \
 sudo dpkg -i vagrant*.deb && \
 sudo apt-get -y install build-essential git ruby lxc redir && \
 vagrant plugin install vagrant-lxc && \
@@ -205,8 +205,8 @@ sudo apt-get install build-essential git ruby lxc redir
 #### Windows 10
 
 1. Install [Git for Windows][git-bash], which installs *Git BASH*.
-2. Install [VirtualBox][vbox-dl] (version >= 5.1.6 but < 5.2).
+2. Install [VirtualBox][vbox-dl] (version == 5.2.6).
-3. Install [Vagrant][vagrant-dl-win] (version 1.8.4-1.8.6, do not use 1.8.7).
+3. Install [Vagrant][vagrant-dl-win] (version 2.0.2, do not use 1.8.7).
 
 (Note: While *Git BASH* is recommended, you may also use [Cygwin][cygwin-dl].
 If you do, make sure to **install default required packages** along with
@@ -663,8 +663,8 @@ macOS.
 On **macOS** this error is most likely to occur with Vagrant version 1.8.7 and
 is a [known issue](https://github.com/mitchellh/vagrant/issues/7997).
 
-The solution is to downgrade Vagrant to version 1.8.6 ([available
+The solution is to downgrade Vagrant to version 2.0.2 ([available
-here](https://releases.hashicorp.com/vagrant/1.8.6/)), or to use your system's
+here](https://releases.hashicorp.com/vagrant/2.0.2/)), or to use your system's
 version of `curl` instead of the one that ships with Vagrant:
 
 ```
@@ -1049,12 +1049,12 @@ for the IP address that means any IP address can connect to your development ser
 
 [cygwin-dl]: http://cygwin.com/
 [vagrant-dl]: https://www.vagrantup.com/downloads.html
-[vagrant-dl-win]: https://releases.hashicorp.com/vagrant/1.8.6/vagrant_1.8.6.msi
+[vagrant-dl-win]: https://releases.hashicorp.com/vagrant/2.0.2/vagrant_2.0.2_x86_64.msi
-[vagrant-dl-macos]: https://releases.hashicorp.com/vagrant/1.8.6/vagrant_1.8.6.dmg
+[vagrant-dl-macos]: https://releases.hashicorp.com/vagrant/2.0.2/vagrant_2.0.2_x86_64.dmg
-[vagrant-dl-deb]: https://releases.hashicorp.com/vagrant/1.8.6/vagrant_1.8.6_x86_64.deb
+[vagrant-dl-deb]: https://releases.hashicorp.com/vagrant/2.0.2/vagrant_2.0.2_x86_64.deb
 [vagrant-lxc]: https://github.com/fgrehm/vagrant-lxc
 [vbox-dl]: https://www.virtualbox.org/wiki/Downloads
-[vbox-dl-macos]: http://download.virtualbox.org/virtualbox/5.1.8/VirtualBox-5.1.8-111374-OSX.dmg
+[vbox-dl-macos]: https://download.virtualbox.org/virtualbox/5.2.6/VirtualBox-5.2.6-120293-OSX.dmg
 [vmware-fusion-dl]: http://www.vmware.com/products/fusion.html
 [vagrant-vmware-fusion-dl]: https://www.vagrantup.com/vmware/
 [avoiding-sudo]: https://github.com/fgrehm/vagrant-lxc#avoiding-sudo-passwords

docs/tutorials/shell-tips.md

@@ -178,7 +178,7 @@ environment:
 
 ```
 sudo apt-get -y purge vagrant && \
-wget https://releases.hashicorp.com/vagrant/1.8.6/vagrant_1.8.6_x86_64.deb && \
+wget https://releases.hashicorp.com/vagrant/2.0.2/vagrant_2.0.2_x86_64.deb && \
 sudo dpkg -i vagrant*.deb && \
 sudo apt-get -y install build-essential git ruby lxc lxc-templates cgroup-lite redir && \
 vagrant plugin install vagrant-lxc && \