fixed install cmd on windows

[onichandame]

Problem

When run on Windows and agreed to install dependencies, a 'ENOENT' error is thrown.

Cause

The child_process.spawn method does not allow alias somehow, e.g. yarn.cmd aliased to yarn. A reference of this issue can be found here

Fix

simply replacing the 'yarnpkg' and 'npm' variables with the full-pathed executable fixes this.

[onichandame]

@fannheyward Thanks for your approval. I just re-tried the script but it seems to be unchanged.

Perhaps the new commit has yet been published to the npm repository.

If possible please tell me your plan on publishing new versions to npm repo.

[fannheyward]

v0.3.1 has published, thanks for your PR.