postMessageToChannel promise returns undefined

[mastef]

bot.postMessageToChannel('channelname', "Some message", params)
	.then(function(data) {
		console.log("slack data", data);
		return data;
	});

data should be the information regarding the posted message, right? But currently I'm just receiving undefined.

I've reviewed the code, and it seems the callback checker is hijacking the return value in https://github.com/mishk0/slack-bot-api/blob/master/index.js#L388-L394

After adding an else { return data.value; } to handle the case where cb is not defined it works for me:

        return this[method](name).then(function(itemId) {
            return this.postMessage(itemId, text, params);
        }.bind(this)).always(function(data) {
            if (cb) {
                cb(data._value);
+           }else{
+               return data._value;
+           }
        });

[mastef]

It might be slightly related to #37 except that the message gets posted here successfully. Just the return value in the promise is missing.