[bug fix] When the environment is Linux/Unix, an exception will be thrown during the merge process due to incorrect paths

src/N_m3u8DL-RE/Util/MergeUtil.cs

@@ -85,9 +85,7 @@ namespace N_m3u8DL_RE.Util
             else
                 div = 200;
 
-            var delimiter=OperatingSystem.IsWindows()?"\\T":"/T";
-
-            string outputName = Path.GetDirectoryName(files[0]) + delimiter;
+            string outputName = Path.Combine(Path.GetDirectoryName(files[0])!, "T");
             int index = 0; //序号
 
             //按照div的容量分割为小数组