chore: added lint stage to npm test

Signed-off-by: Sebastian Haas <sebastian@haas.tech>

package.json

@@ -6,7 +6,8 @@
   "typings": "dist/src/OSMD/OSMD",
   "scripts": {
     "docs": "typedoc --mode file --out build/docs --module commonjs --target ES5 --name opensheetmusicdisplay ./src",
-    "test": "grunt test",
+    "lint": "grunt lint",
+    "test": "npm run lint && grunt test",
     "postinstall": "grunt typings",
     "prepublish": "grunt build:dist"
   },