fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-BSON-561052
- https://snyk.io/vuln/SNYK-JS-EJS-1049328
- https://snyk.io/vuln/SNYK-JS-MINIMATCH-1019388
- https://snyk.io/vuln/SNYK-JS-MINIMIST-559764
- https://snyk.io/vuln/SNYK-JS-MOCHA-561476
- https://snyk.io/vuln/SNYK-JS-MONGODB-473855
- https://snyk.io/vuln/npm:debug:20170905
- https://snyk.io/vuln/npm:extend:20180424
- https://snyk.io/vuln/npm:growl:20160721
- https://snyk.io/vuln/npm:mime:20170907
- https://snyk.io/vuln/npm:minimatch:20160620
- https://snyk.io/vuln/npm:ms:20170412
- https://snyk.io/vuln/npm:qs:20170213
- https://snyk.io/vuln/npm:superagent:20170807
- https://snyk.io/vuln/npm:superagent:20181108

package.json

@@ -5,11 +5,11 @@
   "main": "server.js",
   "dependencies": {
     "chai": "^3.5.0",
-    "chai-http": "^2.0.1",
-    "ejs": "^2.4.1",
+    "chai-http": "^4.0.0",
+    "ejs": "^3.1.6",
     "express": "^4.13.4",
-    "mocha": "^2.4.5",
-    "mongodb": "^2.1.16",
+    "mocha": "^6.2.3",
+    "mongodb": "^3.1.13",
     "morgan": "^1.7.0",
     "object-assign": "4.1.0"
   },