fix index issue with NBA home_points on OT games

[DoubleBarrelBirds]

the home_points index of -1 seems to work, but not for overtime games.

This is the test data I used to validate

data = {'away_points' : [115, 108, 109, 126],
        'home_points' : [116, 121, 117, 133]}

expected_values_df = pd.DataFrame(data, columns = ['away_points', 'home_points'], index=['201810200PHI', '201810200POR', '201904070TOR', '201904050PHO'])

x1 = Boxscore("201810200PHI").dataframe[['away_points', 'home_points']]
x2 = Boxscore("201810200POR").dataframe[['away_points', 'home_points']]
x3 = Boxscore("201904070TOR").dataframe[['away_points', 'home_points']]
x4 = Boxscore("201904050PHO").dataframe[['away_points', 'home_points']]

result_df = x1.append(x2).append(x3).append(x4)
result = result_df.equals(expected_values_df)
result