Update pytest_flask package and remove Python 3.3

Author: Shane DeWael

requirements-dev.txt

@@ -3,7 +3,7 @@ ipdb==0.9.3
 ipython==4.1.2
 pdbpp==0.8.3
 pytest>=3.2.0
-pytest-flask==0.10.0
+pytest-flask>=0.14.0
 pytest-mock>=1.6.3
 pytest-cov==2.5.1
 pytest-pythonpath==0.7.1

tox.ini

@@ -4,7 +4,7 @@
 ; for quality analysis, use `tox -e flake8` or just `flake8 slackeventsapi`
 ; to build the docs, use `tox -e docs`
 envlist=
-    py{276,27,33,34,35,36},
+    py{276,27,34,35,36},
     flake8,
     docs