GoL_fast: Make datacollection import explicit (#199)

Author: EwoutH

examples/conways_game_of_life_fast/model.py

@@ -1,5 +1,6 @@
 import numpy as np
-from mesa import DataCollector, Model
+from mesa import Model
+from mesa.datacollection import DataCollector
 from mesa.space import PropertyLayer
 from scipy.signal import convolve2d