truncate long branch names on MR index

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/projects/merge_requests/_merge_request.html.haml

@@ -11,11 +11,7 @@
         - if merge_request.for_fork?
           %span.light
             #{merge_request.source_project_namespace}:
-          = merge_request.source_branch
-          %i.icon-angle-right.light
-          = merge_request.target_branch
-        - else
-          = merge_request.source_branch
+        = truncate merge_request.source_branch, length: 25
         %i.icon-angle-right.light
         = merge_request.target_branch
   .merge-request-info