patch 8.2.3888: the argument list may contain duplicates

Problem:    The argument list may contain duplicates.
Solution:   Add the :argdedeupe command. (Nir Lichtman, closes #6235)
diff --git a/src/version.c b/src/version.c
index 0809436..78baffd 100644
--- a/src/version.c
+++ b/src/version.c
@@ -750,6 +750,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3888,
+/**/
     3887,
 /**/
     3886,