Directly return matched content instead of explicitely chopping off backticks

https://github.com/dmg01/snippet-bot/blob/7857918d8e390ca9a06294e5dd566626f3037161/bot.js#L112-L119

I think what you need on line 118 is something like
```
var matches = regex.exec(string)
return (matches[1] || [])
```

I'm not sure, it's a bit late here, maybe I'll test this tomorrow after some sleep :P