base/tool: downgrade error to warning

modules/base/tool.go

@@ -186,7 +186,7 @@ func AvatarLink(email string) (url string) {
 		var err error
 		url, err = setting.LibravatarService.FromEmail(email)
 		if err != nil {
-			log.Error(2, "LibravatarService.FromEmail [%s]: %v", email, err)
+			log.Warn("AvatarLink.LibravatarService.FromEmail [%s]: %v", email, err)
 		}
 	}
 	if len(url) == 0 && !setting.DisableGravatar {