chore(package): update @types/express to version 4.17.6

Closes #112

Author: greenkeeper[bot]

package.json

@@ -29,7 +29,7 @@
     "@types/chai": "^4.1.7",
     "@types/debug": "4.1.0",
     "@types/dotenv": "^6.1.0",
-    "@types/express": "4.17.0",
+    "@types/express": "4.17.6",
     "@types/mocha": "^5.2.7",
     "@types/mongodb": "^3.1.14",
     "@types/mongoose": "5.5.7",