Заменяет нерабочую ссылку

fix htmlacademy#27

Author: juwain

Readme.md

@@ -5,7 +5,7 @@
 * [Code Guide](http://codeguide.co) by @mdo
 * [CSS Guidelines](http://cssguidelin.es) by Harry Roberts
 * [Idiomatic CSS](https://github.com/necolas/idiomatic-css) by Nicolas Gallagher
-* [Primer Guidelines](http://primercss.io/guidelines/) by GitHub
+* [Primer Guidelines](https://styleguide.github.com/primer/principles/) by GitHub
 
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