Pyramid-layout broken with pyramid-jinja2 >= 2.0

The template renderers from pyramid-jinja2 >-= 2.0 no longer have a `.template` attribute.
(Instead they have a callable `.template_loader`.)

I’m not absolutely certain that this is not a bug in pyramid-jinja2 rather than pyramid-layout. OTOH, so far as I can tell the only documented API for renderers (as of pyramid 1.5) is `__call__()`.