Enhancement: Single way to authenticate if Face ID or Touch ID enabled

[inPhilly]

• [ X] I have read this issue template and provided all possible information.
• [X ] I'm NOT using CocoaPods.

Hardware / Software

Which version of the library were you using? 0.0.2 - 2017-12-16
Which version of iOS are you running? 11.2
What model of iOS device were you testing on? all on simulator
If using CocoaPods, which version of CocoaPods are you on? n/a

Goals

Enhancement: This is a quote from Apple: "Present people with a single way to authenticate. It's most intuitive when people don't have to choose how to authenticate. Just give them a single option, like Face ID. Offer alternatives, like asking for a username and password, as fallbacks only if the initial method fails." on this page: https://developer.apple.com/ios/human-interface-guidelines/user-interaction/authentication/

It also has two images that show the passcode controller presenting Face ID or Touch ID as the first option, before the passcode number entry view.

Just a thought as to where Apple is proposing we go with these passcode views. Thanks!