Improve the image tag name in the makefile

Created by: LinuxSuRen

See also:

codespace ➜ /workspaces/ks-installer (refactor/remove-devops-crd ✗) $ make build
docker build . --file Dockerfile --tag kubespheredev/ks-installer:refactor/remove-devops-crd-dev
invalid argument "kubespheredev/ks-installer:refactor/remove-devops-crd-dev" for "-t, --tag" flag: invalid reference format
See 'docker build --help'.
make: *** [Makefile:5: build] Error 125

The result with this PR:

docker build . --file Dockerfile --tag kubespheredev/ks-installer:refactor-remove-devops-crd-dev