Require aiohttp != 3.7.4.post0, as aioresponses does not support that version

requirements.txt

@@ -2,7 +2,7 @@
 # should match https://pypi.python.org/pypi names. For the full spec or
 # dependency lines, see https://pip.readthedocs.org/en/1.1/requirements.html
 requests
-aiohttp
+aiohttp != 3.7.4.post0
 ndjson
 plotly
 pandas