Music channel on Discord only accepts www.youtube.com as host name

[simonthor]

Describe the bug
music channel on discord only accepts www.youtube.com host name, not e.g. youtu.be, a shorter version of the same URL.

To Reproduce
Steps to reproduce the behavior:

1. Go to Digital Ungdom's discord server (https://discordapp.com/channels/468044152970674176)
2. Click on #music group (bottom left).
3. Enter $play https://youtu.be/dQw4w9WgXcQ in the text bar and press enter.
4. The message is deleted immediately.

Expected behavior
The music should be played instead of deleting the message.

Screenshots
https://gyazo.com/ff1ce8687001a3f7aa6b64afb8072fc5 (made by @simpmaestro on Discord)

Possible solutions

1. add "youtu.be" to host name check. This solution is simple but not scalable. For example, if we later would like to add a feature where it can play shortened links in general, the list of allowed links would become too long.
2. Check if link contains a video or not. This solution requires a lot more coding but is more scalable. This can for example look for special HTML tags such as <iframe> or

[kelszo]

Another common youtube host is m.youtube.com (for mobiles). The current pull request (#5) should be updated to support this.

[simonthor]

Another common youtube host is m.youtube.com (for mobiles). The current pull request (#5) should be updated to support this.

Good point. I fixed this in the latest commit (see ee54a5b).