node-gyp-bin: fix custom node-gyp env var quoting

npm sets node_config_node_gyp without quotes, so its usage should be
quoted. Indeed, it is a better practice to define environment variables
that contain paths without quotes and quote their usage.

PR-URL: #11158
Credit: @orangemocha
Reviewed-By: @othiym23

bin/node-gyp-bin/node-gyp.cmd

@@ -1,5 +1,5 @@
 if not defined npm_config_node_gyp (
   node "%~dp0\..\..\node_modules\node-gyp\bin\node-gyp.js" %*
 ) else (
-  node %npm_config_node_gyp% %*
+  node "%npm_config_node_gyp%" %*
 )