chore(package): update loopback-connector-mongodb to version 3.9.1

Closes #22

Author: greenkeeper[bot]

package.json

@@ -39,7 +39,7 @@
     "husky": "0.14.2",
     "loopback": "3.8.0",
     "loopback-boot": "2.25.0",
-    "loopback-connector-mongodb": "3.2.0",
+    "loopback-connector-mongodb": "3.9.1",
     "loopback-testing": "1.4.0",
     "mocha": "3.4.2",
     "mocha-sinon": "2.0.0",