This plugin doesn't work without http_proxy

[toru-takahashi]

Currently, the plugin doesn't work when user doesn't use http_proxy.
It looks this change affect it.
fa83a87

irb(main):001:0> (proxy,proxy_port) = ENV['http_proxy'].split(':')
NoMethodError: undefined method `split' for nil:NilClass
    from (irb):1
    from /Users/.../.rbenv/versions/2.3.0/bin/irb:11:in `<main>'
irb(main):002:0>

[toru-takahashi]

This PR would fix this issue.
#11

[nathanhruby]

#12 would also fix this issue, it seems. Either way, #9 seems to add a requirement for a proxy which I think was not the intention.

Would be great to get this fixed.

[nitish661401869]

@memorycraft @mlin could you please let us know when you intend to resolve this issue by merging the requested PR(s) ?

We need the fix for our code to not blow up.

Thanks.