Rename the checkbox css class to prevent it from being overwritten by the same...

Rename the checkbox css class to prevent it from being overwritten by the same named bootstrap class.

app/assets/stylesheets/sections/merge_requests.scss

@@ -29,7 +29,7 @@
       line-height: 20px;
       font-weight: bold;
 
-      .checkbox {
+      .remove_source_checkbox {
         margin: 0;
       }
     }

app/views/projects/merge_requests/show/_mr_accept.html.haml

@@ -18,7 +18,7 @@
             = f.submit "Accept Merge Request", class: "btn btn-create accept_merge_request"
           - if can_remove_branch?(@merge_request.source_project, @merge_request.source_branch) && !@merge_request.for_fork?
             .accept-control
-              = label_tag :should_remove_source_branch, class: "checkbox" do
+              = label_tag :should_remove_source_branch, class: "remove_source_checkbox" do
                 = check_box_tag :should_remove_source_branch
                 Remove source-branch
           .accept-control