Completely move xdist pins in tox.ini. Fixes incorrect installs during testing.

Author: ionelmc

setup.py

@@ -130,7 +130,6 @@ def run(self):
             'fields',
             'hunter',
             'process-tests==2.0.2',
-            'pytest-xdist==1.27.0',
             'six',
             'virtualenv',
         ]

tox.ini

@@ -18,12 +18,13 @@ deps =
     t41: pytest==4.1.1
     t43: pytest==4.3.1
     t44: pytest==4.4.1
+
+    {t310,t40,t41,t43}: pytest-xdist==1.27.0
     t44: pytest-xdist==1.28.0
 
     c44: coverage==4.4.2
     c45: coverage==4.5.3
 pip_pre = true
-
 commands =
     pytest {posargs:-vv}