Run cargo update && cargo upgrade (#716)

The important updates here are the upgrade to Skrifa 0.22.3, and png
0.17.14.

Exactly what that Skrifa update does isn't very clear, since I've not
been able to find fontation's changelog (cc @dfrg). This does mean we
are testing with what our users will actually use in the imminent 0.3.0
release.