fix(package): update debug to version 4.0.0

Closes #16

Author: greenkeeper[bot]

package.json

@@ -22,7 +22,7 @@
   },
   "main": "lib/index.js",
   "dependencies": {
-    "debug": "^2.6.4",
+    "debug": "^4.0.0",
     "depd": "^1.1.0",
     "lodash": "^4.17.4"
   },