Colons in channel names are incorrectly encoded

We have hit an issue whereby colons in channel names are incorrectly encoded and thus the authorisation with the PubNub backend fails.

This commit does not really offer a solution but provides a clearly understandable test case of our problem. I don't intend this to be merged so forgive me the sloppy `puts`.

To see the problem switch to this branch and run `rspec spec/lib/subscribe_event.rb`. The name of the channel is "demo:demo" which is encoded as `demo%253Ademo`. It seems that the colon is encoded twice because the correct encoding would be `demo%3Ademo`.

This is causing our customers to not be able to use this Ruby client. It'd be great if you could provide a fix.

If you have any further questions, please shoot.

Thanks,
Leonard