Fix diff header for discussion

app/assets/stylesheets/base/gl_bootstrap.scss

@@ -182,6 +182,7 @@
     .panel-heading {
       padding: 6px 15px;
       font-size: 13px;
+      font-weight: normal;
       a {
         color: #777;
       }

app/assets/stylesheets/pages/notes.scss

@@ -90,8 +90,13 @@ ul.notes {
 }
 
 // Diff code in discussion view
-.discussion-body .diff-file .line_content {
+.discussion-body .diff-file {
+  .diff-header > span {
+    margin-right: 10px;
+  }
+  .line_content {
     white-space: pre-wrap;
+  }
 }
 
 .diff-file .notes_holder {