adjust gcal plugin's UMD

src/gcal/gcal.js

@@ -8,6 +8,9 @@
 	if (typeof define === 'function' && define.amd) {
 		define([ 'jquery' ], factory);
 	}
+	else if (typeof exports === 'object') { // Node/CommonJS
+		module.exports = factory(require('jquery'));
+	}
 	else {
 		factory(jQuery);
 	}