fix(package): update react-router-dom to version 5.1.1

Closes #41

Author: greenkeeper[bot]

package.json

@@ -10,7 +10,7 @@
     "react": "^15.4.0",
     "react-dom": "^15.4.0",
     "react-router": "^4.0.0",
-    "react-router-dom": "^4.0.0"
+    "react-router-dom": "^5.1.1"
   },
   "scripts": {
     "now-start": "cd build && serve -s ./",