add rule "cargo" to build the kernel

3 jobs for stage5 in 40 seconds (queued for 1 second)
Status Job ID Name Coverage
  Prepare
passed #562036
linux shell
docker

00:00:02

 
  Build
failed #562037
docker
build

00:00:38

 
  Test
skipped #562038
docker
test
 
Name Stage Failure
failed
build Build

error: aborting due to previous error

error: could not compile `eduos-rs`.

To learn more, run the command again with --verbose.
Makefile:35: recipe for target 'cargo' failed
make: *** [cargo] Error 101
ERROR: Job failed: exit code 1