chore(package): update mocha to version 6.2.2

Closes #9

Author: greenkeeper[bot]

package.json

@@ -25,7 +25,7 @@
   },
   "devDependencies": {
     "bindings": "^1.3.0",
-    "mocha": "^5.0.0",
+    "mocha": "^6.2.2",
     "nan": "^2.8.0",
     "nyc": "^12.0.1",
     "ref": "^1.3.5"