Signature validation error.

[Kamalnrf]

I want my bot to accept HTTP requests as well so for now what I'm doing something like this

bot.app.get('/', (req, res) => { //Some other stuff });

Now when I'm trying to do POST request with JSON data I was getting "Couldn't validate the request signature." error so for this I had to remove the middleware.

bot.app._router.stack = bot.app._router.stack.slice(0,2)

What I propose is in _verifyRequestSignature check for webhook if it is not let it go as a normal web request.

[mraaroncruz]

Closing in favor of #84