package.json: lint all .js files

This makes the linting process less prone to miss new (or even
existing) files. Ignoring specific file paths is delegated to the
.eslintignore file in the root directory.

package.json

@@ -14,7 +14,7 @@
     "start": "node index",
     "build": "grunt",
     "test": "HOME=test/fixtures mocha test/**/*.js && npm run lint",
-    "lint": "eslint index.js Gruntfile.js src/ test/ client/ defaults/"
+    "lint": "eslint ."
   },
   "keywords": [
     "browser",