增加vendor

vendor/github.com/silenceper/wechat/v2/util/string.go

@@ -0,0 +1,18 @@
+package util
+
+import (
+	"math/rand"
+	"time"
+)
+
+// RandomStr 随机生成字符串
+func RandomStr(length int) string {
+	str := "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+	bytes := []byte(str)
+	result := []byte{}
+	r := rand.New(rand.NewSource(time.Now().UnixNano()))
+	for i := 0; i < length; i++ {
+		result = append(result, bytes[r.Intn(len(bytes))])
+	}
+	return string(result)
+}