Check for global variable leaks

Author: maltsev

package.json

@@ -9,7 +9,7 @@
     "compile": "rm -f lib/*.js && node_modules/.bin/babel -d lib/ lib/",
     "lint": "node_modules/.bin/eslint *.js lib/*.es6 test/",
     "pretest": "npm run lint && npm run compile",
-    "test": "node_modules/.bin/_mocha --compilers js:babel-core/register",
+    "test": "node_modules/.bin/_mocha --compilers js:babel-core/register --check-leaks",
     "prepublish": "npm run compile"
   },
   "keywords": [