fix(package): update react-dom to version 16.3.2

Closes #3

Author: greenkeeper[bot]

package.json

@@ -15,7 +15,7 @@
     "mobx": "^3.2.1",
     "mobx-react": "^4.2.2",
     "react": "^15.6.1",
-    "react-dom": "^15.6.1",
+    "react-dom": "^16.3.2",
     "react-router": "^4.1.2",
     "simple-oauth2": "^1.3.0",
     "todomvc-app-css": "^2.0.4",