HTTP 404 error for upcoming NCAAB season

[roclark]

Describe the bug
When trying to pull data for the upcoming NCAAB season, a 404 error will be returned as the requested data is not yet available. Currently, the error has the following traceback:

Traceback (most recent call last):
  File "tests/exhaustive/test_ncaab.py", line 7, in <module>
    for team in Teams():
  File "/home/runner/work/sportsreference/sportsreference/sportsreference/ncaab/teams.py", line 999, in __init__
    self._retrieve_all_teams(year)
  File "/home/runner/work/sportsreference/sportsreference/sportsreference/ncaab/teams.py", line 1125, in _retrieve_all_teams
    doc = pq(BASIC_STATS_URL % year)
  File "/opt/hostedtoolcache/Python/3.5.7/x64/lib/python3.5/site-packages/pyquery/pyquery.py", line 223, in __init__
    html = url_opener(url, kwargs)
  File "/opt/hostedtoolcache/Python/3.5.7/x64/lib/python3.5/site-packages/pyquery/openers.py", line 78, in url_opener
    return _requests(url, kwargs)
  File "/opt/hostedtoolcache/Python/3.5.7/x64/lib/python3.5/site-packages/pyquery/openers.py", line 63, in _requests
    resp.reason, resp.headers, None)
urllib.error.HTTPError: HTTP Error 404: Not Found

To Reproduce
Pull any data for NCAAB in the new season.

from sportsreference.ncaab.teams import Teams

for team in Teams():
    print(team.name)

Expected behavior
Either the error will be handled and the code will continue without errors and no data will be retrieved, or the previous year will be queried instead.

Desktop (please complete the following information):

• OS: Ubuntu 18.04 (affects all)
• Sportsreference Version: 0.4.5