Select only a subset of hljs languages (#70)

assets/styles/highlightjs.scss

@@ -1,7 +1,7 @@
 .hljs {
   display: block;
   overflow-x: auto;
-  padding: 0.5em;
+  padding: 0.5rem !important;
   background: #F0F0F0
 }
 
@@ -92,4 +92,4 @@ pre {
     word-break: normal;
     font-family: monospace;
   }
-}
+}