Ice dragon missing `turn_rate`

[ThePython10110]

I spawned a few dragons, then got this error:
draconis/api/behaviors.lua:200: attempt to perform arithmetic on field 'turn_rate' (a nil value)
After looking through the code a bit, it seems like the ice dragon is just missing the turn_rate field.

[BobOmbuzal]

Same as #33
Fixed by #37
Just replace all "self.turn_rate" with "self.turn_rate or 6"