cash-global doesn't work in non-English operating systems

Installing `cash-global` won't work properly in any OS whose language isn't English. That seems to be because of the test for the "Could not find" output of the `where` command in the `bin/preinstall.js` returning false positives in other languages.
I couldn't find it in the original source code though but I certainly don't actually have a grasp of the projects bigger structure.

For example the failing output of `where` in my German Windows looks like this

> INFORMATION: Es konnten keine Dateien mit dem angegebenen Muster gefunden werden.

I'd suggest using the npm `which` package instead since it's going to be included in the application anyways according to #71.