Grammar correction: "View in Gitlab"

Changed to "View on Gitlab"

app/views/layouts/notify.html.haml

@@ -23,4 +23,4 @@
         - if @project
           You're receiving this notification because you are a member of the #{link_to @project.name_with_namespace, project_url(@project)} project team.
         - if @target_url
-          #{link_to "View in GitLab", @target_url}
+          #{link_to "View on GitLab", @target_url}