Fix wrong key name

Rename "repo_url" to "github_url"

Author: shaedrich

topics/unist/index.md

@@ -3,7 +3,7 @@ display_name: Universal Syntax Tree.
 short_description: unist is a specification for syntax trees. It has a big ecosystem of utilities in JavaScript for working with these trees.
 topic: unist
 url: https://unifiedjs.com/
-repo_url: https://github.com/syntax-tree/unist
+github_url: https://github.com/syntax-tree/unist
 related: ast, cst, syntax tree
 ---
 unist is a specification for syntax trees. It has a big ecosystem of utilities in JavaScript for working with these trees. It’s implemented by several other specifications.