Set overflow hidden on status bar

The octicon was causing overflow, which was making the entire view
scroll because the status bar was bigger than the height used by
flexbox.

static/status-bar.css

@@ -5,6 +5,7 @@
   position: relative;
   -webkit-user-select: none;
   cursor: default;
+  overflow: hidden;
 }
 
 .status-bar .git-branch {