flutter Error: Could not resolve the package ‘characters‘ in ‘package:characters/characters.dart‘.

背景：升级flutter为1.20.0，运行项目报错。

解决过程：
修改项目目录android/build.gradle里的maven仓库 无效！！！

flutter的issue搜索问题： Could not resolve the package ‘characters’ in ‘package:characters/characters.dart’.

解决方法：使用命令：
flutter pub cache repair
flutter clean

成功。