Update pytest-xdist to 1.22.1 (#197)

* Update pytest-xdist from 1.22.0 to 1.22.1

requirements/py27-tests.txt

@@ -3,5 +3,5 @@ mozlog==3.7
 pytest==3.4.0
 pytest-metadata==1.5.1
 pytest-selenium==1.11.4
-pytest-xdist==1.22.0
+pytest-xdist==1.22.1
 selenium==3.9.0

requirements/py36-tests.txt

@@ -2,5 +2,5 @@ mock==2.0.0
 pytest==3.4.0
 pytest-metadata==1.5.1
 pytest-selenium==1.11.4
-pytest-xdist==1.22.0
+pytest-xdist==1.22.1
 selenium==3.9.0