remove mCaptcha hyperlink (#593)

causes "mCaptcha" to show up as a instance on api.invidious.io

docs/instances.md

@@ -10,7 +10,7 @@
 
 * [yewtu.be](https://yewtu.be) 🇩🇪 - Source code/changes: https://github.com/yewtudotbe/invidious-custom
 
-* [inv.nadeko.net](https://inv.nadeko.net) 🇨🇱 - Source code/changes: https://git.nadeko.net/Fijxu/invidious - CAPTCHA: [mCaptcha](https://mcaptcha.org/)
+* [inv.nadeko.net](https://inv.nadeko.net) 🇨🇱 - Source code/changes: https://git.nadeko.net/Fijxu/invidious - CAPTCHA: mCaptcha (https://mcaptcha.org/)
 
 * [invidious.nerdvpn.de](https://invidious.nerdvpn.de) 🇺🇦 - Source code/changes: https://github.com/Sommerwiesel/invidious-nerdvpn