fix: update markdown submodule link

Author: maikol-solis

.gitmodules

@@ -242,7 +242,7 @@
 	ignore = dirty
 [submodule "repos/markdown"]
 	path = repos/markdown
-	url = https://github.com/ikatyang/tree-sitter-markdown
+	url = https://github.com/tree-sitter-grammars/tree-sitter-markdown
 	branch = master
 	update = none
 	ignore = dirty