Follow up r15975. Fixed warning on elemental.c. (bugreport:5637)

git-svn-id: https://svn.code.sf.net/p/rathena/svn/trunk@15976 54d463be-8e91-2dee-dedb-b68131a5f0ec

src/map/elemental.c

@@ -9,6 +9,7 @@
 #include "../common/mmo.h"
 #include "../common/showmsg.h"
 #include "../common/utils.h"
+#include "../common/random.h"
 
 #include "log.h"
 #include "clif.h"