Add a way to get gravityform's version (#1883)

* Add a way to get gravityform's version

This can be tested [here](https://about.mattermost.com/blog/)

* Fix a typo, thanks to @kkadosh

src/apps.json

@@ -3396,6 +3396,7 @@
 				"<ul [^>]*class=(?:\"|')[^>]*gform_fields",
 				"<link [^>]*href=(?:\"|')[^>]*wp-content/plugins/gravityforms/css/"
 			],
+			"script": "/wp-content/plugins/gravityforms/js/[^/]+\\.js\\?ver=([\\d.]+)$\\;version:\\1",
 			"icon": "gravityforms.svg",
 			"implies": "WordPress",
 			"website": "http://gravityforms.com"