fix setup.cfg to point to docs/changelog.rst

Author: kokobhara

setup.cfg

@@ -6,7 +6,7 @@ author = Vital Kudzelka
 keywords = pytest, flask, testing
 author_email = vital.kudzelka@gmail.com
 url = https://github.com/pytest-dev/pytest-flask
-long_description = file: README.rst, CHANGELOG.rst, LICENSE
+long_description = file: README.rst, docs/changelog.rst, LICENSE
 description = A set of py.test fixtures to test Flask applications.
 project_urls =
     Source = https://github.com/pytest-dev/pytest-flask