React strict mode compatibility

[jwhiting]

As surfaced in #59, the FirebaseAuth and StyledFirebaseAuth components are not React strict-mode compatible. In particular both of these components fail to render and throw Error: AuthUI instance is deleted!

Unfortunately, React does not currently offer a way for any part of a strict-mode component tree to opt-out of strict mode (per facebook/react#16362), so the only solution for people using this library appears to be turning strict mode off entirely, or going to great lengths to try to wrap the parts of the tree that do not include this component in strict-mode wrappers, which is extremely error-prone.

[jwhiting]

Actually given that #173 may fix this, and has been awaiting merge for a very long time with no activity, I assume this project is dead, and am closing this issue