Support international domain names (IDN)

[crimson-med]

I have recently built a small experimental service to serve dynamic svg images.

I have noticed that when I host the service on a IDN the images are broken on github.com

example code:

![graph](https://avallon.io:8443/user/noimage)
![graph](https://avallon.io:8443/user)

---

![graph](https://火.dev:8443/user/noimage)
![graph](https://火.dev:8443/user)

---

![graph](https://xn--vnx.dev:8443/user/noimage)
![graph](https://xn--vnx.dev:8443/user)

rendered code:

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Would it be possible to get support for IDNs?