Implement quality option for ios

[n1ru4l]

Important:

This pull request is a follow-up to https://github.com/phuochau/react-native-thumbnail/pull/21, please consider merging #21 first.

Code Sample

import RNThumbnail from 'react-native-thumbnail';

RNThumbnail.get(filepath, { quality: 0.1 }).then((result) => {
  console.log(result.path); // thumbnail path
})

[phuochau]

@n1ru4l Seem the example is wrong again? the options should be a parameter of get method?

[n1ru4l]

@phuochau I updated the example, however the code is fully functional