Adding support for .jenkinsfile extension and Jenkinsfile.* filename pattern

So that it will be consistent with the support of Dockerfile.

The file is using tabs AND spaces for indentation, this commit follows the formatting rules defined in .editorconfig (2 spaces).

extensions/groovy/package.json

@@ -13,8 +13,8 @@
 		"languages": [{
 			"id": "groovy",
 			"aliases": ["Groovy", "groovy"],
-			"extensions": [".groovy", ".gvy", ".gradle"],
-			"filenames": [ "Jenkinsfile" ],
+      "extensions": [".groovy", ".gvy", ".gradle", ".jenkinsfile"],
+      "filenamePatterns": ["Jenkinsfile.*"],
 			"firstLine": "^#!.*\\bgroovy\\b",
 			"configuration": "./language-configuration.json"
 		}],