Updated numpy to 1.16.6

The pipeline was crashing due a numpy error that is fixed in version >1.16.
meqtrees_cattery was not happy with numpy > 1.16 due his specification:
pkg_resources.ContextualVersionConflict: (numpy 1.16.6), Requirement.parse('numpy<=1.16'), set(['meqtrees-cattery']))
Edited Dockerfile to change the version on the METADATA