chore(package): update mocha to version 6.2.1

Closes #8

Author: greenkeeper[bot]

package.json

@@ -26,7 +26,7 @@
   "devDependencies": {
     "assume": "~2.0.0",
     "istanbul": "0.4.x",
-    "mocha": "~3.5.0",
+    "mocha": "~6.2.1",
     "pre-commit": "~1.2.0"
   },
   "dependencies": {