Add Makefile / .drone.yml, use go module with vendor (#20)

* add Makefile / .drone.yml, use go module with vendor

* Update .drone.yml

Co-Authored-By: lunny <xiaolunwen@gmail.com>

vendor/gopkg.in/src-d/go-git.v4/plumbing/error.go

@@ -0,0 +1,35 @@
+package plumbing
+
+import "fmt"
+
+type PermanentError struct {
+	Err error
+}
+
+func NewPermanentError(err error) *PermanentError {
+	if err == nil {
+		return nil
+	}
+
+	return &PermanentError{Err: err}
+}
+
+func (e *PermanentError) Error() string {
+	return fmt.Sprintf("permanent client error: %s", e.Err.Error())
+}
+
+type UnexpectedError struct {
+	Err error
+}
+
+func NewUnexpectedError(err error) *UnexpectedError {
+	if err == nil {
+		return nil
+	}
+
+	return &UnexpectedError{Err: err}
+}
+
+func (e *UnexpectedError) Error() string {
+	return fmt.Sprintf("unexpected client error: %s", e.Err.Error())
+}