Update optimizer.py

Author: Evolutionary-Intelligence

pypop7/optimizers/core/optimizer.py

@@ -39,11 +39,6 @@ class Optimizer(object):
     Lectures on convex optimization.
     Berlin: Springer International Publishing.
     https://link.springer.com/book/10.1007/978-3-319-91578-4
-
-    Nesterov, Y. and Spokoiny, V., 2017.
-    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
     """
     def __init__(self, problem, options):
         # problem-related settings