Add back serve-favicon package

For now, our server depends on it.

Author: rylnd

package-lock.json

@@ -26,13 +26,16 @@
     "url": "https://github.com/adorableio/adorable-avatars.git"
   },
   "devDependencies": {
+    "@types/express": "^4.16.1",
     "@types/mocha": "^5.2.6",
     "@types/node": "^11.13.4",
+    "@types/serve-favicon": "^2.2.30",
     "chai": "^4.2.0",
     "colors": "^1.3.3",
     "concurrently": "^4.1.0",
     "find-port": "^2.0.1",
     "mocha": "^6.1.3",
+    "serve-favicon": "^2.5.0",
     "supertest": "^4.0.2",
     "ts-node": "^8.1.0",
     "typescript": "^3.4.3"