Update optimizer.py

Author: Evolutionary-Intelligence

pypop7/optimizers/core/optimizer.py

@@ -44,11 +44,6 @@ class Optimizer(object):
     Random gradient-free minimization of convex functions.
     Foundations of Computational Mathematics, 17(2), pp.527-566.
     https://link.springer.com/article/10.1007/s10208-015-9296-2
-
-    Audet, C. and Hare, W., 2017.
-    Derivative-free and blackbox optimization.
-    Berlin: Springer International Publishing.
-    https://link.springer.com/book/10.1007/978-3-319-68913-5
     """
     def __init__(self, problem, options):
         # problem-related settings