fix(style): prevent scrollbar in code (#18)

That margin was creating horizontal scroll when it wasn't necessary

Author: posva

lib/default-theme/styles/code.styl

@@ -34,7 +34,7 @@
   .highlighted-line
     background-color rgba(0, 0, 0, 66%)
     display block
-    margin 0.1rem -1.8rem 0
+    margin 0.1rem -1.5rem 0
     padding 0.1rem 1.8rem
 
 pre[class="language-js"], pre[class="language-javascript"]