Bump numpy version in rest.

The comment in the file suggest that the numpy version should be the
latest one, it is not.

This would help to make sure that there is no regression in numpy,
and/or that the test suite would catch numpy deprecated functionality.

Author: Carreau

requirements_dev_numpy.txt

@@ -1,6 +1,6 @@
 # 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==1.17.2; python_version > '3.0'
+numpy==1.19.2; python_version > '3.0'
 # don't let pyup change this, needed until we drop support for py27
 numpy==1.16.4; python_version < '3.0' # pyup: ignore