fix(package): update react-dom to version 16.4.0

Closes #16

Author: greenkeeper[bot]

package.json

@@ -36,7 +36,7 @@
   "homepage": "https://github.com/jonathanweiss/react-progress-circle#readme",
   "dependencies": {
     "react": "^15.4.2",
-    "react-dom": "^15.5.1",
+    "react-dom": "^16.4.0",
     "sk-progress-circle": "^0.8.0",
     "skatejs-react-integration": "^2.0.6"
   },