patch 8.2.3101: missing function prototype for vim_round()

Problem:    Missing function prototype for vim_round().
Solution:   Add the prototype
diff --git a/src/version.c b/src/version.c
index 298fd87..600af40 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3101,
+/**/
     3100,
 /**/
     3099,