fix file name add

Author: saturn99

README.md

@@ -4,7 +4,7 @@
 
 This is a collection of numpy exercises from numpy mailing list, stack overflow, and numpy documentation. I've also created some problems myself to reach the 100 limit. The goal of this collection is to offer a quick reference for both old and new users but also to provide a set of exercises for those who teach.
 
-→ [Test them on Binder](http://mybinder.org:/repo/rougier/numpy-100/notebooks/100%20Numpy%20exercises.ipynb)  
+→ [Test them on Binder](http://mybinder.org:/repo/rougier/numpy-100/notebooks/100_Numpy_exercises.ipynb)  
 → [Read them on GitHub](100_Numpy_exercises.md)  
 
 This work is licensed under the MIT license.