Summary:
Starting August 2018, Google Play will require targetSdkVersion 26 for new applications, and November 2018 for application updates.
This PR will use Android build tools 26.0.3 and compilerSdk 26, then support library version 26.0.2 to make targeting 26 easier in the future.
I think this PR will help to people compile and test their applications, thus make transition easier (smoother). Also we'll have opportunity and time to migrate code to target 26.
https://github.com/facebook/react-native/issues/18095
React Native on android must work as usual
Closes https://github.com/facebook/react-native/pull/19257
Differential Revision: D8010354
Pulled By: mdvacca
fbshipit-source-id: 63ba03585e918b38c2a2adb5d2f2e85d7ce46fae