lib: add .json suffix for explicit require

Multiple reports of this failing, seems to be due to node wrapping tools
that mess with the require extensions. So let's be explicit about it.

PR-URL: #1787
Reviewed-By: Reviewed-By: Richard Lau <riclau@uk.ibm.com>

lib/node-gyp.js

@@ -51,7 +51,7 @@ var proto = Gyp.prototype
  * Export the contents of the package.json.
  */
 
-proto.package = require('../package')
+proto.package = require('../package.json')
 
 /**
  * nopt configuration definitions