Remove async from getAllGenericPasswordServices (#464)
Remove async from getAllGenericPasswordServices (#464)

Removed async from getAllGenericPasswordServices to fix 
```
 ERROR  Could not get all keys. TypeError: ReactNativeKeychain.getAllGenericPasswordServices is not a function. (In 'ReactNativeKeychain.getAllGenericPasswordServices()', 'ReactNativeKeychain.getAllGenericPasswordServices' is undefined)
```
oblador/react-native-keychain,oblador/react-native-keychain,oblador/react-native-keychain,oblador/react-native-keychain,oblador/react-native-keychain,oblador/react-native-keychain