docs: update URL of comments of AsyncStorage.js (#348)

Replace invalid URL

Author: jopemachine

lib/AsyncStorage.js

@@ -31,7 +31,7 @@ To fix this issue try these steps:
 
   • If you are using CocoaPods on iOS, run \`pod install\` in the \`ios\` directory and then rebuild and re-run the app.
 
-  • If this happens while testing with Jest, check out docs how to integrate AsyncStorage with it: https://github.com/react-native-community/async-storage/blob/LEGACY/docs/Jest-integration.md
+  • If this happens while testing with Jest, check out docs how to integrate AsyncStorage with it: https://github.com/react-native-community/async-storage/blob/master/docs/Jest-integration.md
 
 If none of these fix the issue, please open an issue on the Github repository: https://github.com/react-native-community/react-native-async-storage/issues 
 `);