fix(git): add vendor in .gitignore

vendor/github.com/gin-contrib/sse/writer.go

@@ -1,24 +0,0 @@
-package sse
-
-import "io"
-
-type stringWriter interface {
-	io.Writer
-	WriteString(string) (int, error)
-}
-
-type stringWrapper struct {
-	io.Writer
-}
-
-func (w stringWrapper) WriteString(str string) (int, error) {
-	return w.Writer.Write([]byte(str))
-}
-
-func checkWriter(writer io.Writer) stringWriter {
-	if w, ok := writer.(stringWriter); ok {
-		return w
-	} else {
-		return stringWrapper{writer}
-	}
-}