Fixed required python version

setup.cfg

@@ -7,7 +7,7 @@ description-file = README.md
 description-content-type = text/markdown
 license = Apache-2.0
 home-page = https://github.com/kotnik/ynab-weekly-spending
-python_requires = '>=2.6, <3'
+python_requires = >=2.6, <3
 classifier =
     Development Status :: 5 - Production/Stable
     Environment :: Console