Pin jinja2 to <3.0
Pin jinja2 to <3.0

Jinja2 3.0 drops support for python 3.5 and Sphinx doens't have a pin.
Markupsafe was also unbounded by jinja2, which means an incompatible
version is now pulled in and we need to put a ceiling pin on that as
well.

markupsafe>=1.1,<2.0
jinja2>=2.3,<3.0

boto/botocore,pplu/botocore