Fix retrocompatibility

Author: Tanguy Damart

bluepyopt/deapext/optimisations.py

@@ -284,7 +284,7 @@ def run(self,
         else:
             pop = self.toolbox.population(n=offspring_size)
 
-        stats = deap.tools.Statistics(key=lambda ind: ind.fitness.reduce)
+        stats = deap.tools.Statistics(key=lambda ind: ind.fitness.sum)
         import numpy
         stats.register("avg", numpy.mean)
         stats.register("std", numpy.std)