js: Use 'npm start' to run 'grunt watch'

js/README.md

@@ -69,7 +69,7 @@ You can now run the tests:
 
 To run tests automatically when you save a file:
 
-    npm run-script watch
+    npm start
 
 To run tests, concatenate, minify the source, and update the JavaScript files
 in `mopidy/frontends/http/data/`:

js/package.json

@@ -31,6 +31,6 @@
   "scripts": {
     "test": "grunt test",
     "build": "grunt build",
-    "watch": "grunt watch"
+    "start": "grunt watch"
   }
 }