Add flutter --update-packages

Otherwise, the analyze would fail.

Author: liyuqian

.cirrus.yml

@@ -58,6 +58,7 @@ task:
         cd $FRAMEWORK_PATH/flutter
         rm -rf bin/cache/pkg/sky_engine
         cp -r $ENGINE_PATH/src/out/host_debug_unopt/gen/dart-pkg/sky_engine bin/cache/pkg/
+        bin/flutter --update-packages
         bin/flutter analyze --dartdocs --flutter-repo --local-engine=host_debug_unopt
       test_framework_script: |
         cd $FRAMEWORK_PATH/flutter/packages/flutter