Use correct JWT auth

Author: Niko Lehtovirta

lib/sheets.js

@@ -6,7 +6,7 @@ var request = require('request');
 
 
 function authorize(options) {
-  var authClient = new google.auth.JWT(
+  var authClient = new google.Auth.JWT(
     options.email,
     null,
     options.key,