docs: Update changelog for Zulip Server 2.1.6 release.

docs/overview/changelog.md

@@ -156,6 +156,11 @@ in bursts.
   system was always a hack, was only ever used for one endpoint, and
   did not provide a measureable latency benefit over HTTP/2.
 
+### 2.1.6 -- 2020-06-17
+
+- Fixed use of Python 3.6+ syntax in 2.1.5 release that prevented
+  installation on Ubuntu Xenial.
+
 ### 2.1.5 -- 2020-06-16
 
 - CVE-2020-12759: Fix reflected XSS vulnerability in Dropbox webhook.

version.py

@@ -10,7 +10,7 @@ if os.path.exists(zulip_git_version_file):
             ZULIP_VERSION = version
 
 LATEST_MAJOR_VERSION = "2.1"
-LATEST_RELEASE_VERSION = "2.1.5"
+LATEST_RELEASE_VERSION = "2.1.6"
 LATEST_RELEASE_ANNOUNCEMENT = "https://blog.zulip.org/2019/12/13/zulip-2-1-released/"
 LATEST_DESKTOP_VERSION = "5.2.0"