MNT: Adjust test tolerance
MNT: Adjust test tolerance

Looks like the newest matplotlib tweaked the end of the lines being
drawn, so slightly bump up the tolerance.

jrleeman/MetPy,ahaberlie/MetPy,ShawnMurd/MetPy,Unidata/MetPy,Unidata/MetPy,jrleeman/MetPy,ahaberlie/MetPy,dopplershift/MetPy,dopplershift/MetPy