tox: Update pytest to 2.8.3.

- add __name__ attribute to testcases in TestCaseFunction to support the
  @unittest.skip decorator on functions and methods.
- collecting tests if test module level obj has __getattr__().
- don't collect tests if their failure cannot be reported correctly e.g. they
  are a callable instance of a class.
- fixed internal error when filtering tracebacks where one entry belongs to a
  file which is no longer available.
- enhancement made to highlight in red the name of the failing tests so
  they stand out in the output.
- minor fixes for interaction with OS X El Capitan system integrity
  protection

tox.ini

@@ -26,7 +26,7 @@ deps =
     parse==1.6.6
     parse-type==0.3.4
     py==1.4.30
-    pytest==2.8.2
+    pytest==2.8.3
     pytest-bdd==2.15.0
     pytest-catchlog==1.2.0
     pytest-cov==2.2.0
@@ -153,7 +153,7 @@ deps =
     execnet==1.4.1
     py==1.4.30
     pyflakes==1.0.0
-    pytest==2.8.2
+    pytest==2.8.3
     pytest-cache==1.0
     pytest-flakes==1.0.1
 commands =
@@ -168,7 +168,7 @@ deps =
     execnet==1.4.1
     pep8==1.6.2
     py==1.4.30
-    pytest==2.8.2
+    pytest==2.8.3
     pytest-cache==1.0
     pytest-pep8==1.0.6
 commands =
@@ -184,7 +184,7 @@ deps =
     execnet==1.4.1
     mccabe==0.3.1
     py==1.4.30
-    pytest==2.8.2
+    pytest==2.8.3
     pytest-cache==1.0
     pytest-mccabe==0.1
 commands =