Investigate connecting to emulators

[jhuleatt]

Description

fixes #459

• [x] Reproduce the issue
  • [x] Update ReactFire Firestore test suite so that it connects to emulators the way we recommend in the docs
  • [x] Show that tests fail when we do so
  • [ ] Investigate why tests fail and identify a fix
• [ ] Fix the issue
  • [ ] Update Firestore test suite to confirm fix works
  • [ ] Update the rest of the ReactFire test suite with the fix
  • [ ] Update docs with new emulator connection instructions