tox: Update pytest to 2.8.5.

- fixed issue where class attributes injected during collection could break pytest.
- precompute junitxml chunks instead of storing the whole tree in objects
- fix ``pytest.deprecated_call()`` receiving multiple arguments
  (Regression introduced in 2.8.4).

tox.ini

@@ -26,7 +26,7 @@ deps =
     parse==1.6.6
     parse-type==0.3.4
     py==1.4.31
-    pytest==2.8.4
+    pytest==2.8.5
     pytest-bdd==2.15.0
     pytest-catchlog==1.2.1
     pytest-cov==2.2.0
@@ -155,7 +155,7 @@ deps =
     execnet==1.4.1
     py==1.4.31
     pyflakes==1.0.0
-    pytest==2.8.4
+    pytest==2.8.5
     pytest-cache==1.0
     pytest-flakes==1.0.1
 commands =
@@ -170,7 +170,7 @@ deps =
     execnet==1.4.1
     pep8==1.6.2
     py==1.4.31
-    pytest==2.8.4
+    pytest==2.8.5
     pytest-cache==1.0
     pytest-pep8==1.0.6
 commands =
@@ -186,7 +186,7 @@ deps =
     execnet==1.4.1
     mccabe==0.3.1
     py==1.4.31
-    pytest==2.8.4
+    pytest==2.8.5
     pytest-cache==1.0
     pytest-mccabe==0.1
 commands =