Adding fullstop to test doc, to appease codacy

tests/py37_asyncio.py

@@ -121,7 +121,7 @@ async def double(i):
 
 @mark.asyncio
 async def test_gather(capsys):
-    """Test asyncio gather"""
+    """Test asyncio gather."""
     res = await gather(list(map(double, range(30))))
     _, err = capsys.readouterr()
     assert '30/30' in err