Fixed example in README

Hi,

This is my first time using your module and I think there is a tiny error in the README.

If I got it right, the default value for `install` is [false](https://github.com/mzgol/check-dependencies/blob/master/lib/check-dependencies.js#L36) but from the examples one could think the inverse.

Great work btw!

Regards,
Guilherme