Issue with prettier-loader and *.vue files

[MahdiZerara]

If you know how to fix the issue, make a pull request instead.

• [ ] I tried using the latest stable version of prettier-loader
• [ ] I've read readme

Select one of these and delete the others:

If asking a question:

• [ ] Question: ...
• [ ] Code (if necessary) below:

_If reporting a bug:_
Good morning and thank you for this wonderful tool! I just want to bring to your attention that this loader doesn't work properly on *.vue files. It actually doesn't recognize the syntax and confuse it with *.js files. Could you please provide a fix for that! 

- [ ] Steps to repeat:
If you try to add this loader to Storybook Webpack configuration, it will alter the vue files and generate a syntax error  
- [ ] Code (if necessary) below:
```js

• [ ] Expected behavior:

• It should prettify *.vue files

• [ ] Observed behavior:

• It is not prettifying *.vue files and it outputs a run error!

[MahdiZerara]

Feel free to reach out if the bug is unclear!