Treat .webmanifest files as JSON

Web App Manifest files (having `webmanifest`¹ as the recommended
file extension and `application/manifest+json`¹ as the recommended
media type) use the JSON² format.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

¹ https://w3c.github.io/manifest/#media-type-registration
² https://w3c.github.io/manifest/#abstract

See also: https://w3c.github.io/manifest/

extensions/json/package.json

@@ -28,10 +28,12 @@
 					".jshintrc",
 					".jscsrc",
 					".eslintrc",
-					".babelrc"
+					".babelrc",
+					".webmanifest"
 				],
 				"mimetypes": [
-					"application/json"
+					"application/json",
+					"application/manifest+json"
 				],
 				"configuration": "./json.configuration.json"
 			}
@@ -131,4 +133,4 @@
 		"vscode-languageclient": "^2.2.1",
 		"vscode-extension-telemetry": "^0.0.5"
 	}
-}
+}