Removed execa dependency

[mackermans]

Replaced with custom childprocess exec implementation

[davesnx]

I like it brah 👍

So sad that execa didn't work with 0.10.40 and also more sad that atom uses node -v 0.10

[davesnx]

Could you also, publish a patch?

PS: and we could remove the is-path dependency, it's quite trivial.
It's actually merge this checks:
https://github.com/jonschlinkert/is-invalid-path/blob/master/index.js +
https://github.com/jonschlinkert/is-glob/blob/master/index.js +
https://github.com/jonschlinkert/is-extglob/blob/master/index.js

What do you think @mackermans ?

[mackermans]

@davesnx I think we can keep it for now, it's a small dependency. I also added the strip-eof dependency so we're not zero-dependency anyway.

[davesnx]

Could you update travis to add 0.10 also?