Fix "requirePaddingNewlinesInBlock" typo in README documentation

- `requirePaddingNewlinesInBlock` should have been`requirePaddingNewlinesInBlocks`

tried using `"requirePaddingNewlinesInBlock": "true"` and jscs threw an error, so I looked into the source and determined it could be a typo in readme.

cc. @mikesherov 

btw, nice library :)