Update React peer dependency to 16.8.x

Author: markerikson

package.json

@@ -36,7 +36,7 @@
     "coverage": "codecov"
   },
   "peerDependencies": {
-    "react": "^16.4.0-0",
+    "react": "^16.8.4",
     "redux": "^2.0.0 || ^3.0.0 || ^4.0.0-0"
   },
   "dependencies": {