Add horizontal scrolling to code blocks.

app/assets/stylesheets/generic/common.scss

@@ -333,6 +333,10 @@ table {
   margin-bottom: 9px;
 }
 
+.wiki .code {
+  overflow-x: auto;
+}
+
 .footer-links a {
   margin-right: 15px;
 }

app/assets/stylesheets/generic/highlight.scss

@@ -59,6 +59,7 @@
   box-shadow: none;
   background: $box_bg;
   padding: 1em;
+  overflow-x: auto;
 
   code {
     font-family: $monospace_font;