allow flag --target in build process

docker.go

@@ -44,6 +44,7 @@ type (
 		Tags        []string // Docker build tags
 		Args        []string // Docker build args
 		ArgsEnv     []string // Docker build args from env
+		Target      string   // Docker build target
 		Squash      bool     // Docker build squash
 		Pull        bool     // Docker build pull
 		Compress    bool     // Docker build compress
@@ -204,6 +205,9 @@ func commandBuild(build Build) *exec.Cmd {
 	for _, arg := range build.Args {
 		args = append(args, "--build-arg", arg)
 	}
+	if build.Target != "" {
+		args = append(args, "--target", build.Target)
+	}
 
 	labelSchema := []string{
 		fmt.Sprintf("build-date=%s", time.Now().Format(time.RFC3339)),