Googling, the release notes don’t mention iOS version. However, for 1.6.4, it specifies support for iOS 10.3:
I think you should at least update to 1.6.4 for iOS 10.3 support, but if it were me I would move to 1.6.5 or 1.7.0 (since 1.6.6 seems like it’s never coming out of beta). As a personal aside, I have it on my roadmap to update to 1.7.x in Q4.