Fixed #51 EnvCommand display and save error messages to init file bug

if $version and PHPBREW_PHP env not exists, EnvCommand will throw exception, but exception message will been saved to ~/.phpbrew/init file.

This is cause phpbrew switch-off always display 'Could not open input file: version:' message or each time user logined and ~/.phpbrew/bashrc loaded.

Signed-off-by: Rack Lin <racklin@gmail.com>