As the results of "uname -s" command is like the below on MSYS2 on
Windows Terminal,

MSYS_NT-10.0-22621

This patch fixes the Flutter command working on this kind of systems.
Signed-off-by: Deokgyu Yang <secugyu@gmail.com>
Signed-off-by: Deokgyu Yang <secugyu@gmail.com>