Tmux error is not well handled which throws TypeError: a bytes-like object is required, not 'str'

[qinfeng]

Tmux error is not well handled which cause bridgy tmux session not open.

env:
macOS 10.13 + python3.6.5

bridgy config:

 tmux:
   layout:
       logger:
           - cmd: split-window -h
           - cmd: split-window -h
           - cmd: split-window -h
             run: tail -f /var/log/syslog
           - cmd: set-window-option synchronize-panes on

bridgy command:

bridgy ssh -tl logger core -I mysource

error:

Traceback (most recent call last):
  File "/Users/qinfeng/.local/share/virtualenvs/bridgy-5NqTP_ZY/bin/bridgy", line 11, in <module>
    load_entry_point('bridgy', 'console_scripts', 'bridgy')()
  File "/Users/qinfeng/Projects/github/bridgy/bridgy/__main__.py", line 425, in main
    handler(args, config)
  File "/Users/qinfeng/Projects/github/bridgy/bridgy/utils.py", line 34, in wrapper
    func(*args,**kwargs)
  File "/Users/qinfeng/Projects/github/bridgy/bridgy/__main__.py", line 218, in ssh_handler
    tmux.run(config, commands, args['-w'], layout, args['-d'], args['-s'])
  File "/Users/qinfeng/Projects/github/bridgy/bridgy/tmux.py", line 20, in run
    with TmuxSession(commands=commands, in_windows=in_windows, layout_cmds=layout_cmds, dry_run=dry_run, sync=sync) as tmux:
  File "/Users/qinfeng/Projects/github/bridgy/bridgy/tmux.py", line 58, in __enter__
    self.tmux(*cmd)
  File "/Users/qinfeng/Projects/github/bridgy/bridgy/tmux.py", line 118, in tmux
    repr(std_err.strip("\n").replace("\n",', ')),
TypeError: a bytes-like object is required, not 'str'

It looks like std_err returned by python subprocess pipe is in bytes type which needs to be decoded to str obj