Fix URL in readme

Author: aibaars

ruby/ql/lib/codeql/ruby/frameworks/stdlib/README.md

@@ -1,3 +1,3 @@
 This directory contains QL modules that model classes and modules in the Ruby standard library.
 Files are named after the most common or top-level class in each library.
-See https://docs.ruby-lang.org/en/3.1/doc/standard_library_rdoc.html for a full list.
+See https://docs.ruby-lang.org/en/3.1/standard_library_rdoc.html for a full list.