Bump Android build tools to 28.0.3 in Dockerfile (#30832)
Bump Android build tools to 28.0.3 in Dockerfile (#30832)

Bumps the Android build tools to 28.0.3 instead of 28.0.0 in the Dockerfile, since that is what flutter doctor wants.
flutter/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,cbracken/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,cbracken/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter