Merge branch 'add_diff_note_hover_size' into 'master'

Keep add-diff-note button the same size on hover. Fixes #2497

Removes the overridden `font-size` and `width` so the button inherits size on hover. See #2497 for screenshots of prior behavior.

See merge request !1285

app/assets/stylesheets/pages/notes.scss

@@ -235,8 +235,6 @@ ul.notes {
     filter: alpha(opacity=0);
 
     &:hover {
-      width: 38px;
-      font-size: 20px;
       background: $gl-info;
       color: #FFF;
       @include show-add-diff-note;