Upgrade react-router to v5

Author: lindapaiste

package-lock.json

@@ -221,8 +221,8 @@
     "react-markdown": "^6.0.3",
     "react-redux": "^7.2.4",
     "react-responsive": "^8.2.0",
-    "react-router": "^4.3.0",
-    "react-router-dom": "^4.3.0",
+    "react-router": "^5.3.4",
+    "react-router-dom": "^5.3.4",
     "react-split-pane": "^0.1.92",
     "react-tabs": "^2.3.1",
     "react-transition-group": "^4.4.2",