Change master in links to HEAD

Author: wooorm

readme.md

@@ -220,11 +220,11 @@ abide by its terms.
 
 [license]: license
 
-[contributing]: https://github.com/syntax-tree/.github/blob/master/contributing.md
+[contributing]: https://github.com/syntax-tree/.github/blob/HEAD/contributing.md
 
-[help]: https://github.com/syntax-tree/.github/blob/master/support.md
+[help]: https://github.com/syntax-tree/.github/blob/HEAD/support.md
 
-[coc]: https://github.com/syntax-tree/.github/blob/master/code-of-conduct.md
+[coc]: https://github.com/syntax-tree/.github/blob/HEAD/code-of-conduct.md
 
 [unist]: https://github.com/syntax-tree/unist