Merge branch '15104-mobile-comment-bug' into 'master'

Discussion note icon shows up when you click on diff on touch screen

Fixes #15104 

* Fix bug that stopped discussion note button from showing up on iOS
* Shifted button a few `px` to fix slight cutoff
<div>
<img src="/uploads/9d507091f33aa69ef68323386bf3a5c2/Screen_Shot_2016-04-15_at_12.08.46_PM.png" width="300px">
<img src="/uploads/a964a2a46636cbe4593abf272b5796f7/Screen_Shot_2016-04-15_at_12.11.40_PM.png" width="300px">
</div>

See merge request !3755

app/assets/stylesheets/pages/diff.scss

@@ -34,6 +34,7 @@
     background: #fff;
     color: #333;
     border-radius: 0 0 3px 3px;
+    -webkit-overflow-scrolling: auto;
 
     .unfold {
       cursor: pointer;

app/assets/stylesheets/pages/notes.scss

@@ -295,7 +295,7 @@ ul.notes {
     padding: 4px;
     font-size: 16px;
     color: $gl-link-color;
-    margin-left: -60px;
+    margin-left: -56px;
     position: absolute;
     z-index: 10;
     width: 32px;