Fixed empty literal detection
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>
```

pwmckenna/eslint-plugin-react,lencioni/eslint-plugin-react,petersendidit/eslint-plugin-react,mathieumg/eslint-plugin-react,teambox/eslint-plugin-react,AlexKVal/eslint-plugin-react,evocateur/eslint-plugin-react,kevinold/eslint-plugin-react,Khan/eslint-plugin-react,benmosher/eslint-plugin-react,edge/eslint-plugin-react,markdalgleish/eslint-plugin-react,xjamundx/eslint-plugin-react,kylpo/eslint-plugin-react,yannickcr/eslint-plugin-react,epmatsw/eslint-plugin-react