IP by hostname error fix

As discussed here: https://github.com/luisivan/pebble-slides/issues/9
I thought it would be better not to presume we should do this different way just for Macs, but instead to fall back on it if we get that exception (that way it might just catch a problem on other systems too).
I'm not a Python programmer, so I hope this is OK! If not, please feel free to rip apart!