Avoid pytest 3 warning (#517)

* Avoid pytest warning

* Upgrade pytest min version in tox.ini
diff --git a/setup.cfg b/setup.cfg
index b4deb77..14ed149 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,5 +1,5 @@
-[pytest]
-minversion = 2.8.5
+[tool:pytest]
+minversion = 3.0.1
 strict = true
 testpaths = tests
 
diff --git a/tox.ini b/tox.ini
index 661e5ca..8701977 100644
--- a/tox.ini
+++ b/tox.ini
@@ -7,7 +7,7 @@
 passenv = ARCHFLAGS CFLAGS LC_ALL LDFLAGS PATH LD_LIBRARY_PATH TERM
 deps =
     coverage>=4.2
-    pytest>=2.8.5
+    pytest>=3.0.1
     cryptographyMaster: git+https://github.com/pyca/cryptography.git
     cryptographyMinimum: cryptography<1.4
 setenv =