Refactor repository in package.json

Author: wooorm

package.json

@@ -9,7 +9,7 @@
     "range",
     "mdast"
   ],
-  "repository": "https://github.com/syntax-tree/mdast-util-heading-range",
+  "repository": "syntax-tree/mdast-util-heading-range",
   "bugs": "https://github.com/syntax-tree/mdast-util-heading-range/issues",
   "author": "Titus Wormer <[email protected]> (http://wooorm.com)",
   "contributors": [