chore(package): update react-router to version 5.1.2

Closes #553

Author: greenkeeper[bot]

package.json

@@ -80,7 +80,7 @@
     "react-dom": "^16.0.0",
     "react-hot-loader": "3.1.3",
     "react-prism": "^4.3.0",
-    "react-router": "^4.1.1",
+    "react-router": "^5.1.2",
     "react-router-dom": "^4.1.1",
     "react-syntax-highlighter": "^5.5.2",
     "react-tap-event-plugin": "^3.0.2",