removed constraint on nevergrad, since the old one isn't compatible with numpys > 1.20.0

requirements.txt

@@ -6,7 +6,7 @@ scikit-learn
 scikit-image>=0.14
 pandas>=0.8.1
 PyYAML>=5.1, !=5.4.*
-nevergrad<=0.4.2
+nevergrad
 dicom2nifti
 medpy
 SimpleITK<2.1.0