add manual pretender shutdown to fix acceptance tests

[kevinansfield]

no issue

• ensure our mirage server is shutdown during app teardown in acceptance tests
• a recent update to Pretender contained a breaking change that throws an error when multiple pretender instances exist
• using mirage in acceptance tests was triggering the error

[robneville73]

@kevinansfield tried to do the same thing and it's not fixing the issue...any idea what I might be missing?

[trek]

Pretender 1.4.1 is released and only warns now. To be fair: starting several pretender servers has never been allowed and shutting down is specifically called out in the README as a requirement. We only started preventing it because people forgetting this requirement was causing other issues.

[acburdine]

@kevinansfield Do we still want this? If so it might be a good idea to update the TODO comment :)

[acburdine]

@kevinansfield I can either merge this now or close it as the same change is present in #37 as part of the mirage update. I'm fine with either :)

[kevinansfield]

@acburdine let's merge this now as it makes the test logs on Travis rather noisy. I've updated the comment to remove the TODO as the upstream "fix" was to make it a warning rather than an error meaning this is still necessary