apps: Properly name Linux repo key.

Tiny remove-newline fix as well.

(imported from commit 5c68635973366b9ff68a96fdca3bf3196583d690)

templates/zerver/apps.html

@@ -72,15 +72,14 @@
         <h3>Debian and Ubuntu</h3>
         We have an APT repository for Zulip, so adding and installing the app is easy:
         <div class="codehilite"><pre>wget https://zulip.com/dist/keys/user-apt.asc
-cat user.asc | sudo apt-key add -
+cat user-apt.asc | sudo apt-key add -
 sudo apt-add-repository http://apt.zulip.com/user/
 sudo apt-get update
 {% if not_enterprise %}
 sudo apt-get install zulip-desktop
 {% else %}
 sudo apt-get install zulip-desktop-sso
-{% endif %}
-</pre></div>
+{% endif %}</pre></div>