Update dependency react-native to v0.81.0

Author: renovate[bot]

package.json

@@ -8,7 +8,7 @@
   },
   "dependencies": {
     "react": "16.3.2",
-    "react-native": "0.39.2",
+    "react-native": "0.81.0",
     "react-native-scrollable-tab-view": "0.7.4",
     "react-native-sensors": "next"
   },