chore(package): update mocha to version 6.1.2

Closes #9

Author: greenkeeper[bot]

package.json

@@ -10,7 +10,7 @@
   "devDependencies": {
     "chai": "~3.5.0",
     "istanbul": "~0.4.5",
-    "mocha": "~3.2.0",
+    "mocha": "~6.1.2",
     "mocha-lcov-reporter": "~1.2.0",
     "pre-commit": "~1.2.0",
     "sinon": "~1.17.6",