RocketChat connection issue.

[aon4o]

With the current version of the project, I couldn't make the package send a message to RocketChat.
Whatever I make, RocketChat returns error 405.
In my opinion the problem is with the way that the connection is made.
I've created a pull request #23, that changes the URL for sending messages, tested it, and it seems to work.

I'm looking forward to using the project so if there's anything else I can help with feel free to contact me.