Use actual GitLab URL for test assertion

Assert the full GitLab root URL, including the port, instead of using a
regexp to tolerate whatever port is returned.

spec/helpers/gitlab_markdown_helper_spec.rb

@@ -594,7 +594,9 @@ describe GitlabMarkdownHelper do
     end
 
     it "should generate absolute urls for emoji" do
-      markdown(':smile:').should match(%r{src="http://localhost(:\d+)?/assets/emoji/smile.png})
+      markdown(':smile:').should(
+        include(%(src="#{Gitlab.config.gitlab.url}/assets/emoji/smile.png))
+      )
     end
 
     it "should generate absolute urls for emoji if relative url is present" do