Add extension onto flexboxgrid import (#93)

Makes it easier to mock when testing, since testing setups have a role saying to mock out '*.css'

Author: nathanstitt

src/classNames.js

@@ -1,4 +1,4 @@
-import styles from 'flexboxgrid';
+import styles from 'flexboxgrid/dist/flexboxgrid.css';
 
 export default function getClass(className) {
   return (styles && styles[className]) ? styles[className] : className;