Test broken: number_of_colors should return 0 without tty

[fwenzel]

def test_number_of_colors_without_tty():
    """``number_of_colors`` should return 0 when there's no tty."""
    # Hypothesis: once setupterm() has run and decided the tty supports 256
    # colors, it never changes its mind.
    raise SkipTest

This test is currently skipped. Should find a way to fix that.

[jquast]

directly related to issue #33

[jquast]

resolved by 'blessed-integration' branch.