chore(package): update mocha to version 6.1.3

Closes #17

Author: greenkeeper[bot]

package.json

@@ -30,7 +30,7 @@
   "devDependencies": {
     "chai": "^4.1.2",
     "istanbul": "^0.4.5",
-    "mocha": "^5.0.0",
+    "mocha": "^6.1.3",
     "tom-sawyer": "^0.1.4"
   }
 }