fix扩展名可能为大写

pkg/util/util.go

@@ -3,10 +3,11 @@ package util
 import (
 	"errors"
 	"path/filepath"
+	"strings"
 )
 
 func ValidateFilename(filename string) error {
-	switch filepath.Ext(filename) {
+	switch filepath.Ext(strings.ToLower(filename)) {
 	case ".pdf", ".doc", ".jpg", ".gif", ".png", ".jpeg",
 		".docx", ".xls", ".xlsx", ".zip", ".rar", ".7z", ".txt":
 		return nil