core: fix the HOME dir detection on Windows 7

Author: TooTallNate

lib/node-gyp.js

@@ -41,7 +41,7 @@ function Gyp () {
   // set the dir where node-gyp dev files get installed
   // TODO: make this configurable?
   //       see: https://github.com/TooTallNate/node-gyp/issues/21
-  var homeDir = process.env.HOME
+  var homeDir = process.env.HOME || process.env.USERPROFILE
   this.devDir = path.resolve(homeDir, '.node-gyp')
 
   this.commands = {}