Ask people to remove 1.8 ruby to prevent issues

CHANGELOG

@@ -7,6 +7,7 @@ v 5.3.0
   - Improve sign-in page if ldap enabled
   - Respect newlines in wall messages
   - Generate the Rails secret token on first run
+  - Rename repo feature
 v 5.2.0
   - Turbolinks

doc/install/installation.md

@@ -69,6 +69,10 @@ does not ship with one. The recommended mail server is postfix and you can insta
 # 2. Ruby
+Remove old 1.8 ruby if present
+
+    sudo apt-get remove ruby1.8
+
 Download and compile it:
     mkdir /tmp/ruby && cd /tmp/ruby