Fix "Requires main queue setup" warning

[andriichernenko]

This fixes the warning in console which is produced by react-native-version-check@2.1.0 running with React Native 0.51 on iOS:

Module RNVersionCheck requires main queue setup since it overrides `constantsToExport` 
but doesn't implement `requiresMainQueueSetup`. In a future release React Native will 
default to initializing all native modules on a background thread unless explicitly opted-out of.

[kimxogus]

Thank you for contribution 👍
You can ignore CI failure. There's some issue in test settings.
Your changes looks great, but I have a question. Does this pr works with RN<0.51?

[andriichernenko]

I haven't checked, but the change is purely additive, so I suppose earlier versions will just ignore this method.

[andriichernenko]

Okay, I verified the change against RN 0.44, 0.48, 0.49 and 0.50. As expected, no weird stuff.

[kimak]

@andriichernenko thanks for the changes.
@kimxogus possible to see this merged and npm publish ?

This fix is really the way to go with new versions of React Native.
Look at react-native-maps same changes: https://github.com/react-community/react-native-maps/pull/1873/files

[kimxogus]

Sorry for late response. I'm quite busy thesedays :-(
@andriichernenko Thank you for verification! I'll merge right now
@kimak I'll publish new version within a few hours.