UserId module references usersync and not userSync

[ETNOL]

@idettman Should this be using userSync and not usersync?

Originally posted by @ETNOL in #3424 (comment)

[bretg]

Wow - that's an unfortunate one. Hard to believe no one caught that in several reviews. Ultimately it's my fault because that's how the original issue specified it. #3046

At least the documentation is aligned with the code.

@idettman - please modify the code to look for both usersync and userSync, explaining in a comment that a future major release will deprecate the lowercase version.

[bretg]

Confirmed that this is part of PR 3831. Closing this issue.