"Ambiguous use of operator '<'" in DateAndTime.swift

[leroykim]

Hello,

First of all, thank you for great iOS SMART on FHIR framework.

When I build SoF-Demo (https://github.com/smart-on-fhir/SoF-Demo), I got "Ambiguous use of operator '<'" error in DateAndTime.swift.

My Xcode version is 9.2 (9C40b) and here is the screenshot :

And I have one more thing to ask. Is there a plan to update to support Swift4? I got so many warnings when I build project.