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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_tmuxinator_dir():
 """ Return tmuxinator configuration directory. Checks for ``TMUXINATOR_CONFIG`` environmental variable. Returns ------- str : absolute path to tmuxinator config directory See Also -------- :meth:`tmuxp.config.import_tmuxinator` """

    if 'TMUXINATOR_CONFIG' in os.environ:
        return os.path.expanduser(os.environ['TMUXINATOR_CONFIG'])

    return os.path.expanduser('~/.tmuxinator/')