add missing const

If you want to declare a pointer which the address pointed to is constant,
you should declare it as like `static const char *const var = "...";`.

This commit supplies missing `const` and prevents some programming
error in the future.

src/mplayer.c

@@ -14,7 +14,7 @@ static void mk_mplayer_armor(struct monst *, short);
  * Keep in alphabetical order within teams.
  * Same first name is entered once within each team.
  */
-static const char *developers[] = {
+static const char *const developers[] = {
     /* devteam */
     "Alex",    "Dave",   "Dean",    "Derek",   "Eric",    "Izchak",
     "Janet",   "Jessie", "Ken",     "Kevin",   "Michael", "Mike",