Given that we bumped deps to fairly modern distros with the
python3 change, I think this is safe. gtk 3.22 is from sep 2016, it's
in debian9 and fedora 25+, which seems fine for our needs.
We need to bump the gtk dep to at least 3.10 for GtkRevealer usage,
and I want to bump the pygobject higher to drop some bug workarounds.
But since the oldest thing I have that meets those requirements is
RHEL/Centos 7.3 which is at 3.14 for both, set those as the minimum
versions since that's what I'll be testing against. They are still
1.5 years old and only a bit over a year newer than the previous
versions, so it's not a huge change.
Cole Robinson