chore(package): update react-dom to version 16.8.6

Closes #7

Author: greenkeeper[bot]

package.json

@@ -34,7 +34,7 @@
     "postcss-loader": "^2.0.6",
     "postcss-nested": "^3.0.0",
     "raw-loader": "^0.5.1",
-    "react-dom": "^15.6.1",
+    "react-dom": "^16.8.6",
     "storybook-readme": "^3.0.5",
     "style-loader": "^0.19.0",
     "webpack": "^3.3.0",