Update requirements_dev_numpy.txt

Author: Carreau

requirements_dev_numpy.txt

@@ -1,6 +1,7 @@
 # Break this out into a separate file to allow testing against
 # different versions of numpy. This file should pin to the latest
 # numpy version.
-numpy==1.19.2; python_version > '3.0'
+numpy==1.19.2; python_version >= '3.6'
+numpy==1.17.2; python_version < '3.6'
 # don't let pyup change this, needed until we drop support for py27
 numpy==1.16.4; python_version < '3.0' # pyup: ignore