CI: xfail on numpy 1.18
xref #29053 

i think this addresses the failing azure builds, not sure about Travis.

Will open an issue for a longer-term fix.
cool, merge on green.

do you need to port this to 0.25.2 as well? Probably need to backport. Restarted the stalled 3.8 build. updated the 3.8 build to use the numpy wheel