Today Apple released a minor update for iOS 11.3.1 for iPhone, iPad, and iPod Touch. This update fixes problems with third party iPhone 8 screen replacements as well as updates the security of your device.
Also released was Security Update 2008-001 for macOS 10.13.4.
You can update your iOS device in Settings > General > Software Update
You can update your Mac by clicking the Apple logo icon > App Store > Updates