Change master in links to HEAD

Author: wooorm

readme.md

@@ -295,15 +295,15 @@ abide by its terms.
 
 [author]: https://wooorm.com
 
-[contributing]: https://github.com/syntax-tree/.github/blob/master/contributing.md
+[contributing]: https://github.com/syntax-tree/.github/blob/HEAD/contributing.md
 
-[support]: https://github.com/syntax-tree/.github/blob/master/support.md
+[support]: 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
 
 [hyperscript]: https://github.com/dominictarr/hyperscript
 
-[virtual-hyperscript]: https://github.com/Matt-Esch/virtual-dom/tree/master/virtual-hyperscript
+[virtual-hyperscript]: https://github.com/Matt-Esch/virtual-dom/tree/HEAD/virtual-hyperscript
 
 [react]: https://reactjs.org/docs/glossary.html#react-elements