sysutils/py-plumbum: update to 1.9.2.

ChangeLog:

• CLI: Progress now has a clear keyword that hides the bar on completion
• CLI: Progress without clear now starts on next line without having to manually add '\n'.
• Commands: modifiers now accept a timeout parameter (#281)
• Commands: BG modifier now allows stdout/stderr redirection (to screen, for example) (#258)
• Commands: Modifiers no longer crash on repr (#262)
• Remote: nohup works again, typo fixed (#261)
• Added better support for SunOS and other OS's. (#260)
• Colors: Context manager flushes stream now, provides more consistant results
• Other smaller bugfixes, better support for Python 3.6+