fix modular document code. (#409)

docs/documentation/overview/modular.html

@@ -25,7 +25,7 @@ doc-subtab: modular
         Simply <strong>import</strong> the utilities dependencies, and then the files you need directly:
       </p>
 {% highlight sass %}
-@import "bulma/sass/utilities/_all
+@import "bulma/sass/utilities/_all"
 @import "bulma/sass/grid/columns"
 {% endhighlight %}
       <p>