Fix broken link to pytest.org (exercism#1901)

cmccandless · web-flow · commit ede3016eae91 · 2019-08-07T15:22:06.000-04:00
diff --git a/docs/TESTS.md b/docs/TESTS.md
@@ -1,6 +1,6 @@
 ## Installing `pytest`
 
-We recommend you install [pytest](http://pytest.org/latest/) and
+We recommend you install [pytest](http://pytest.org/en/latest/) and
 [pytest-cache](http://pythonhosted.org/pytest-cache/). `pytest` is a testing
 tool that will give you more flexibility over running your unit tests.
 
