Set proper name for subcommand task

Rename class name of subcommand task to Task, so that help messages for
this subcommand are proper formatted.

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
Update version output format, and related test case

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
v1.0.0-rc2

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>