跳过flutter私有库发布验证

使用方法

1、把文件拷贝到dart-sdk/bin/snapshots中

2、修改dart-sdk/bin/pub文件用记事本打开

3、SNAPSHOT="$BIN_DIR/snapshots/pub.dart.snapshot" 修改为SNAPSHOT="$BIN_DIR/snapshots/mypub.dart.snapshot"