Add more spacing between MR widget and tabs

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

app/assets/stylesheets/pages/merge_requests.scss

@@ -91,8 +91,6 @@
 
 @media(min-width: $screen-sm-max) {
   .merge-request .merge-request-tabs{
-    margin: 20px 0;
-
     li {
       a {
         padding: 15px 40px;
@@ -102,6 +100,11 @@
   }
 }
 
+.merge-request .merge-request-tabs{
+  margin-top: 30px;
+  margin-bottom: 20px;
+}
+
 .mr_source_commit,
 .mr_target_commit {
   .commit {