fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/npm:moment:20170905

Latest report for dadi/api-mongodb:
https://snyk.io/test/github/dadi/api-mongodb

package.json

@@ -22,7 +22,7 @@
   "license": "ISC",
   "dependencies": {
     "@dadi/metadata": "^1.0.0",
-    "convict": "4.0.0",
+    "convict": "4.0.2",
     "debug": "3.1.0",
     "mongodb": "2.2.x"
   },