Update pytest to 4.1.0 (#4427)

And use 'match' instead of 'message' with pytest.raises(), since the
former is actually what we should have been using all along.

See:
pytest-dev/pytest#3974

requirements/dev.txt

@@ -1,8 +1,8 @@
 # Dependencies needed only for development/testing.
 
-pytest==4.0.2 \
-    --hash=sha256:f812ea39a0153566be53d88f8de94839db1e8a05352ed8a49525d7d7f37861e9 \
-    --hash=sha256:f689bf2fc18c4585403348dd56f47d87780bf217c53ed9ae7a3e2d7faa45f8e9
+pytest==4.1.0 \
+    --hash=sha256:3e65a22eb0d4f1bdbc1eacccf4a3198bf8d4049dea5112d70a0c61b00e748d02 \
+    --hash=sha256:5924060b374f62608a078494b909d341720a050b5224ff87e17e12377486a71d
 
 django-debug-toolbar==1.11 \
     --hash=sha256:c2b0134119a624f4ac9398b44f8e28a01c7686ac350a12a74793f3dd57a9eea0 \

tests/test_setup.py

@@ -12,7 +12,7 @@ def test_block_unmocked_requests():
     """Ensure the `block_unmocked_requests` fixture prevents requests from hitting the network."""
     url = 'https://example.com'
 
-    with pytest.raises(RuntimeError, message='Tests must mock all HTTP requests!'):
+    with pytest.raises(RuntimeError, match='Tests must mock all HTTP requests!'):
         fetch_text(url)
 
     with responses.RequestsMock() as rsps: