Update aiohttp to latest release

[bnwlkr]

We're currently using aiohttp 3.6.2 which has some deprecation warnings in Python 3.8.

venv/lib/python3.8/site-packages/aiohttp/helpers.py:107
 /Users/bnwlkr/Leonidas/venv/lib/python3.8/site-packages/aiohttp/helpers.py:107: DeprecationWarning: "@coroutine" decorator is deprecated since Python 3.8, use "async def" instead
   def noop(*args, **kwargs):  # type: ignore

test/test_course.py::TestCourse::test_create_invalid_code
test/test_course.py::TestCourse::test_create_invalid_section
test/test_course.py::TestCourse::test_create_valid_course
test/test_course.py::TestCourse::test_create_valid_section
test/test_utils.py::TestUtils::test_find_courses_found
test/test_utils.py::TestUtils::test_find_courses_invalid_course
test/test_utils.py::TestUtils::test_find_courses_section
 /Users/bnwlkr/Leonidas/venv/lib/python3.8/site-packages/aiohttp/connector.py:964: DeprecationWarning: The loop argument is deprecated since Python 3.8, and scheduled for removal in Python 3.10.
   hosts = await asyncio.shield(self._resolve_host(

test/test_course.py::TestCourse::test_create_invalid_code
test/test_course.py::TestCourse::test_create_invalid_section
test/test_course.py::TestCourse::test_create_valid_course
test/test_course.py::TestCourse::test_create_valid_section
test/test_utils.py::TestUtils::test_find_courses_found
test/test_utils.py::TestUtils::test_find_courses_invalid_course
test/test_utils.py::TestUtils::test_find_courses_section
 /Users/bnwlkr/Leonidas/venv/lib/python3.8/site-packages/aiohttp/locks.py:21: DeprecationWarning: The loop argument is deprecated since Python 3.8, and scheduled for removal in Python 3.10.
   self._event = asyncio.Event(loop=loop)

-- Docs: https://docs.pytest.org/en/stable/warnings.html

Apparently, the next version of aiohttp will have the fix. We can just wait for that to be release on PyPi.