chore: lint JS files in root directory

Not a huge deal since these files are trivial, but important if
they ever grow.

commitlint.config.js

@@ -1 +1,3 @@
+'use strict';
+
 module.exports = { extends: ['@commitlint/config-conventional'] };

index.js

@@ -1,2 +1,4 @@
+'use strict';
+
 module.exports = require('./lib/queue');
 module.exports.Job = require('./lib/job');

package.json

@@ -51,7 +51,7 @@
     "sinon": "^7.4.2"
   },
   "scripts": {
-    "lint": "eslint lib test",
+    "lint": "eslint lib test *.js",
     "pretest": "npm run lint",
     "test": "NODE_ENV=test mocha --exit",
     "coveralls": "istanbul cover ./node_modules/mocha/bin/_mocha --report lcovonly -- --exit -R spec && cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js && rm -rf ./coverage",