Switch testenv deps to .[test] instead of an explicit list so the list of test deps in setup.py becomes the single source of truth for test deps.

tox.ini

@@ -3,21 +3,7 @@ envlist = flake8,py27,py33,py34,py35,py36,pre-commit,pypy
 skipsdist = true
 
 [testenv]
-deps=
-    aniso8601
-    pytest>=2.7.2
-    graphql-core>=1.1
-    promise>=2.0
-    graphql-relay>=0.4.5
-    six
-    blinker
-    singledispatch
-    snapshottest
-    mock
-    pytz
-    iso8601
-    pytest-benchmark
-    pytest-mock
+deps = .[test]
 setenv =
      PYTHONPATH = .:{envdir}
 commands=