Fixed empty literal detection

Should ignore any literal nodes that are purely whitespace.
That way simply splitting a node accross multiple lines doens't get reported.

```javascript
<div>
  {'test'}
</div>
```

Author: CalebMorris

lib/rules/no-literals.js

@@ -22,7 +22,7 @@ module.exports = function(context) {
 
     Literal: function(node) {
       if (
-        /[\S]/.test(node.value) &&
+       !/^[\s]+$/.test(node.value) &&
         node.parent &&
         node.parent.type !== 'JSXExpressionContainer'
       ) {