Feature: adds prettier command

[sidferreira]

That's a humble suggestion.
As I worked, I missed a lot this command...

[thymikee]

Thanks for the PR.
However that's not necessary, since you can run yarn lint --fix to fix all Prettier errors, they're autofixable :)

[thymikee]

Feel free to add that to contributing guide, that may be a good idea :)

[sidferreira]

@thymikee I really added eslint and prettier to my workflow. But I keep them separated as sometimes I know there are errors and I just want to fix the code :)

[thymikee]

In this project prettier and eslint are integrated and they shouldn't collide.