ThreadManager.m uses `jsBundleURLForBundleRoot:fallbackResource`, which no longer exists in RN 68

[RustyTheBoyRobot]

Using this library in a React Native 0.68 app, I get the following build error in XCode:

/Users/joltdev/code/jolt/universal/node_modules/react-native-threads/ios/ThreadManager.m:23:61: No visible @interface for 'RCTBundleURLProvider' declares the selector 'jsBundleURLForBundleRoot:fallbackResource:'

Based on this comment by a RN dev, it seems that the fallbackResource is gone and should be removed.

[RustyTheBoyRobot]

I can't tell for sure, but this might be the root cause of both of these issues:

• Using main bundle instead of thread bundle in iOS release mode (react-native 0.68.1) #139
• Support new architecture #145

[jacobp100]

I'm working on supporting this over on my fork https://github.com/jacobp100/react-native-webworker

I haven't got Android working yet