fix: `grunt shell:checkAdb` handles OS and platform the right way

There was a lot of misunderstanding about `grunt phonegap:check` just because I didn't handle `shell:checkAdb` the right way.
It is now independent of OS and platform and display warning messages instead
of errors.

Closes #32
Merge branch 'development'
release 0.1.7
Changelog not working
Merge branch 'master' of github.com:dsimard/grunt-angular-phonegap