Bug in onebox - link being rendered as a Gist when it isn't

[techAPJ (Arpit Jalan)]

@techAPJ

We can add medium.com to the list of domains to ignore canonical tag

Done via:

https://github.com/discourse/discourse/commit/11a07b37e15f20f5de960243b9ad611fd477af6b

Example:

https://medium.com/pragmatic-programmers/circuit-breakers-and-you-ab1281c88f99