Grab the latest here:
Android:
On GitHub –https://github.com/forcedotcom/SalesforceMobileSDK-Android/tree/v6.0.0
On npm – https://npmjs.org/package/forcedroid
On Bintray jCenter – https://bintray.com/forcedotcom/salesforcemobilesdk
iOS:
On GitHub –https://github.com/forcedotcom/SalesforceMobileSDK-iOS/tree/v6.0.0
On npm – https://npmjs.org/package/forceios
Hybrid:
On npm – https://npmjs.org/package/forcehybrid
React Native:
On npm – https://npmjs.org/package/forcereact
Release Notes:
Android –https://github.com/forcedotcom/SalesforceMobileSDK-Android/tree/v6.0.0#whats-new-in-60
iOS –https://github.com/forcedotcom/SalesforceMobileSDK-iOS/tree/v6.0.0#whats-new-in-60