Fix: ravens specified as hostile on Medusa's Island could be peaceful

Noticed when testing the recent bec de corbin change which makes ravens
generate as peaceful; if you happened to enter medusa-3 while wielding
one, all the ravens are peaceful. Even without one, if you entered the
level as a neutral character, some of them would randomly be peaceful
due to matching alignment. But in the medusa-3.lua file, the ravens are
all unconditionally flagged as hostile.

The reason for this behavior is that the lua loading code does not
recognize "hostile" (instead peaceful=0 needs to be set), so it does
nothing and leaves the ravens to generate as if it had been unspecified.
It appeared to affect only these ravens; no other des.monster() uses
hostile=1 instead of peaceful=0.

This bug has been around in the 3.7 development branch since the change
to Lua, but doesn't happen in 3.6 because the des parser does interpret
"hostile" as meaning never peaceful.

I considered augmenting lspo_monster so that it could handle "hostile"
and treat it like peaceful=0, but figure it's probably better not to
have two different booleans that control the same flag (what if someone
specified peaceful = 1 and hostile = 1?)

dat/medusa-3.lua

@@ -132,7 +132,7 @@ des.monster("water nymph")
 des.monster("water nymph")
 
 for i=1,30 do
-   des.monster({ id = "raven", hostile = 1 })
+   des.monster({ id = "raven", peaceful = 0 })
 end
 
 --#medusa-3.lua