Merge branch 'fix/avatar_relative_url' into 'master'

Fix Avatar and Relative URL

Fixes https://github.com/gitlabhq/gitlabhq/issues/7270

Instead of `URI::join` use a simple join with a slash. This is how all other places in GitLab join URLs and it doesn't muck with the relative path.

See merge request !144

app/models/user.rb

@@ -471,7 +471,7 @@ class User < ActiveRecord::Base
   def avatar_url(size = nil)
     if avatar.present?
-      URI::join(gitlab_config.url, avatar.url).to_s
+      [gitlab_config.url, avatar.url].join("/")
     else
       GravatarService.new.execute(email, size)
     end