Fix Time.now casting causing false positive in verify_at

[kevinreedy]

Fixes #353

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[anakinj]

Im wondering if the condition should be inclusive (>=) to handle cases where the verification happen on the same second the token has been issued.

Also a test verifying the "same-second" token would be good. Mocking the Time.now.to_i in a test could be a way to tackle the different cases.