Support noclobber option of bash

[norioxkimura]

The line of .pythonbrew/etc/bashrc:

        cat /dev/null > "$PATH_HOME_ETC/venv.run"

should be changed to:

        cat /dev/null >| "$PATH_HOME_ETC/venv.run"

When noclobber option is set by 'set -o noclobber', redirections to existing files fail. '>|' overrides this behavior.