Fixed issue with python 3.5 numpy/pandas versions conflict

Author: Sylvain MARIE

setup.cfg

@@ -32,9 +32,9 @@ setup_requires =
     setuptools_scm
 install_requires =
     # otherwise pyitlib leads to dtype assertion errors with int32/int64
-    numpy>=1.16.6
+    numpy>=1.15
     # for some reason on conda 3.5 pandas 0.24+ does not install
-    pandas>=0.22
+    pandas>=0.21
     pyitlib
     pathlib2;python_version<'3.2'
 tests_require =