Fix minor typos in contributing guide

CONTRIBUTING.rst

@@ -111,12 +111,12 @@ Testing tips
 ----------------
 You can test your project using any specific combination of python, django and django cms.
 
-For example ``tox -epy3.7-django30-cms37`` runs the tests on python 3.7, Django 3.0 and django CMS 3.7.
+For example ``tox -epy37-django30-cms37`` runs the tests on python 3.7, Django 3.0 and django CMS 3.7.
 
 As the project uses `pytest <https://pytest.org/>`_ as test runner, you can pass any pytest option by setting the
 ``PYTEST_ARGS`` environment variable, usually by prepending to the ``tox`` command. Example::
 
-    PYTEST_ARGS=" -s  tests/test_plugins.py::PluginTest -p no:warnings" tox -epy3.7-django30-cms37
+    PYTEST_ARGS=" -s  tests/test_plugins.py::PluginTest -p no:warnings" tox -epy37-django30-cms37
 
 
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