DEPS: unpin Matplotlib
This fails make check.
I think the matplotlib version should be pinned and match the version tag that is shown on the cheatsheets. That way, the cheatsheets will be built with a definite version of matplotlib. The matplotlib version can be bumped, along with version tag on cheatsheets, using the bump2version utility.
Yes, make check fails because the installed matplotlib version does not match the cheatsheets version tag.
Fair enough.
I also added a section to the read me documenting how to use bump2version.
I'm going to close this in favour of other more recent PRs to bump the MPL version.