[requires.io] dependency update (#152)

tox.ini

@@ -14,7 +14,7 @@ passenv =
 deps =
     pytest==6.0.1
     pytest-cov==2.10.1
-    pytest-xdist==2.0.0
+    pytest-xdist==2.1.0
 commands =
     pytest --cov-report=xml  --cov-report=term --cov=hyperframe {posargs}