Run `pub get` if flutter_tools.stamp changes (#3206)
Run `pub get` if flutter_tools.stamp changes (#3206)

This will help folks run pub get after they upgrade their flutter.git
revision.
turnidge/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,cbracken/flutter,Hixie/flutter,aghassemi/flutter,Hixie/flutter,Hixie/flutter,Hixie/flutter,turnidge/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,aghassemi/flutter,aghassemi/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,turnidge/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,aghassemi/flutter,turnidge/flutter,cbracken/flutter,tvolkert/flutter,turnidge/flutter,tvolkert/flutter,cbracken/flutter