support delete multi env (#331)

* support delete multi env

* fix golint

pkg/commands/env.go

@@ -137,12 +137,14 @@ func DeleteEnv(ctx context.Context, args []string, ioStreams cmdutil.IOStreams)
 	if len(args) < 1 {
 		return fmt.Errorf("you must specify env name for vela env delete command")
 	}
-	envName := args[0]
-	msg, err := oam.DeleteEnv(envName)
-	if err == nil {
+	for _, envName := range args {
+		msg, err := oam.DeleteEnv(envName)
+		if err != nil {
+			return err
+		}
 		ioStreams.Info(msg)
 	}
-	return err
+	return nil
 }
 
 func CreateOrUpdateEnv(ctx context.Context, c client.Client, envArgs *types.EnvMeta, args []string, ioStreams cmdutil.IOStreams) error {