Add a way to detect Jekyll via html (#1894)

* Add a way to detect Jekyll via html

This can be tested [here](https://www.blackhoodie.re/archive/),
and on any Jekyll blog that you might encounter

* A lot of github pages are created with "Jekyll Now"

This can be tested [here](http://www.unicorn-engine.org/download/)

src/apps.json

@@ -4186,6 +4186,10 @@
 				"11"
 			],
 			"icon": "Jekyll.png",
+			"html": [
+				"Powered by <a href=\"https?://jekyllrb.com\"[^>]*>Jekyll</",
+				"<!-- Created with Jekyll Now -"
+			],
 			"meta": {
 				"generator": "Jekyll (v[\\d.]+)?\\;version:\\1"
 			},