patch 8.2.3101: missing function prototype for vim_round()

Problem:    Missing function prototype for vim_round().
Solution:   Add the prototype

Author: brammool

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3101,
 /**/
     3100,
 /**/