fix callback benchmark

Author: viblo

benchmarks/pymunk-collision-callback.py

@@ -8,10 +8,9 @@
 b = pymunk.Body(1,10)
 c = pymunk.Circle(b, 5)
 s.add(b, c)
-h = s.on_collision(None, None)
 def f(arb, s, data):
     return False
-h.pre_solve = f
+s.on_collision(pre_solve=f)
 """
 
 print(min(timeit.repeat("s.step(0.01)", setup=s, repeat=10)))