Salesforce Summer '19 was pushed to orgs this past weekend and the remaining orgs will be updated this coming weekend (June 14/15th). Details can be found on page 5.
Requirements for the Salesforce Mobile App - Apple iOS
The Salesforce for iOS mobile app will now require iOS 12.0 and higher in v220.0, which will be released alongside Salesforce Summer '19. Users of prior versions of iOS will be able to continue using the current version of the mobile app, but will not be able to upgrade to v220.0 (Summer '19 release). See page 6 for details.
Requirements for the Salesforce Mobile App - Android
Salesforce App for Android is retiring support for Android 5.0 with the Summer '19 release. You will be required to use Android 6.0 or higher. Customers using Android 5.0 will not be able to upgrade to v220.0 (Summer '19 release) or do a fresh install of the app. If the app is already installed, they can continue using it, but they should be advised to plan an upgrade due to the OS no longer receiving security updates from Google. See page 7 for details.