Adds z-index to code block language ribbon

Author: locks

app/styles/components/_highlight.scss

@@ -100,6 +100,7 @@
     @include size(52px 20px);
     background: 0 0 no-repeat;
     background-size: 52px 20px;
+    z-index: 1000;
   }
 
   &.javascript .ribbon,