patch 8.0.1233: typo in dos installer

Problem:    Typo in dos installer.
Solution:   Remove comma.
diff --git a/src/dosinst.c b/src/dosinst.c
index 5a4caac..94e8669 100644
--- a/src/dosinst.c
+++ b/src/dosinst.c
@@ -86,7 +86,7 @@
 enum
 {
     mouse_xterm = 1,
-    mouse_mswin,,
+    mouse_mswin,
     mouse_default
 };
 char	*(mouse_choices[]) =