mockUseFlags should return an empty object

[hjoelh]

Requirements

• [x] I have added test coverage for new or changed functionality
• [x] I have followed the repository's pull request submission guidelines
• [ ] I have validated my changes against all supported platform versions sorry not sure what this means ^

Related issues https://github.com/launchdarkly/jest-launchdarkly-mock/issues/55

Describe the solution you've provided When jest-launchdarkly-mock is added to a jest config, useFlags() calls will now return an empty object by default, which matches its actual implementation

Additional context

• Updated SDK contributor's guide link as current one is dead
• Modified 'reset all flag mocks' test to better represent the affect resetLDMocks() has on mockUseFlags

Thanks! 😀

[louis-launchdarkly]

Hello @hjoelh, thank you for the contribution! I am sorry for the wait - the main developer for jest-launchdarkly-mock is OOO right now, but we will look at this when he is back.