Refactors #validate_otp_token_with_drift

Added

• Appraisal suite.
• Mongoid specs.

Changed

• Refactors #validate_otp_token_with_drift from #15.
• Upgraded rotp dependency to ~> 5.1.

Update rails, symmetric-encryption, and rotp dependencies

• Relaxed Rails dependency to ~> 6.1.
• Upgraded symmetric-encryption dependency to 4.3.0
• Upgraded rotp dependency to ~> 4.0.

Test suite migrated to RSpec

Prepare 0.2.0 for release & switch to CircleCI (#7)

* Switch from Travis to CircleCI

* Updates gem  version to 0.2.0

Initial Release

v0.1.1

Update devise dependency