Update bill.js to make it say the username instead of bill

[ghost]

this will make it kinda more useful & fun

[rayzr522]

Hmmm... maybe this should be an option for the command rather than the default, since the images are originally intended to say Bill? But I certainly would have no problem with this being an option.

EDIT: If you can make this an option and commit that, I will accept the PR. Also, don't just concatenate msg.author.username onto the URL, who knows what Unicode chars they might be using. Use encodeURIComponent(msg.author.username) instead.