Make --color and --no-color exclusive

Signed-off-by: Yusuke Kuoka <ykuoka@gmail.com>

pkg/app/validate_config.go

@@ -0,0 +1,11 @@
+package app
+
+import "errors"
+
+func ValidateConfig(conf ApplyConfigProvider) error {
+	if conf.NoColor() && conf.Color() {
+		return errors.New("--color and --no-color cannot be specified at the same time")
+	}
+
+	return nil
+}