installation failes on windows : --msvs_version npm flag ignored during binding build

When installing via npm with the "--msvs_version" option it is ignored.

This is due to custom install script in package.json, which should be replaced with the automatic node-gyp call performed by node which passed the npm option automatically.

npm searches for binding.gyp and automatically calls node-gyp with the appropriate options.
(https://npmjs.org/doc/json.html)