update mssql drive to last working version 20180314172330-6a30f4e59a44 (#7306)

vendor/github.com/denisenkom/go-mssqldb/tran.go

@@ -1,6 +1,7 @@
+package mssql
+
 // Transaction Manager requests
 // http://msdn.microsoft.com/en-us/library/dd339887.aspx
-package mssql
 
 import (
 	"encoding/binary"
@@ -16,7 +17,18 @@ const (
 	tmSaveXact      = 9
 )
 
-func sendBeginXact(buf *tdsBuffer, headers []headerStruct, isolation uint8,
+type isoLevel uint8
+
+const (
+	isolationUseCurrent     isoLevel = 0
+	isolationReadUncommited          = 1
+	isolationReadCommited            = 2
+	isolationRepeatableRead          = 3
+	isolationSerializable            = 4
+	isolationSnapshot                = 5
+)
+
+func sendBeginXact(buf *tdsBuffer, headers []headerStruct, isolation isoLevel,
 	name string) (err error) {
 	buf.BeginPacket(packTransMgrReq)
 	writeAllHeaders(buf, headers)