chore(package): update mocha to version 6.1.0

Closes #269

Author: greenkeeper[bot]

package.json

@@ -61,7 +61,7 @@
     "istanbul": "^0.4.5",
     "loopback": "^3.16.2",
     "loopback-datasource-juggler": "^3.13.0",
-    "mocha": "^4.0.1",
+    "mocha": "^6.1.0",
     "rsvp": "4.7.0",
     "semantic-release": "^12.2.2",
     "standard": "^10.0.3",