chore(package): update mocha to version 6.1.1

Closes #24

Author: greenkeeper[bot]

package.json

@@ -37,7 +37,7 @@
   "devDependencies": {
     "husky": "^1.0.0",
     "lint-staged": "^4.2.1",
-    "mocha": "^5.0.0",
+    "mocha": "^6.1.1",
     "prettier-standard": "^6.0.0",
     "semantic-release": "^7.0.1",
     "standard": "^11.0.0"