TST: xfail unreliable parallel coordinates sorted label test
merging this; we are hiding another plot related failure: https://ci.appveyor.com/project/pandas-dev/pandas/build/1.0.7819/job/yf9n5cg2xr08l4a8

cc @jorisvandenbossche @TomAugspurger  Is there an issue for that failure? not that i have seen

maybe a matotlib change in version triggers this?