Duplicated description for `<` and `<=` comparator rule functions

[aSemy]

The rules for both < and <= both say First argument is less than the second.

https://github.com/yaml/yaml-grammar/blob/15047828ace28d09594d3553b90b165fef60634b/yaml-spec-1.2.yaml#L257-L261

I presume this is a mistake, and it should be:

  #   * (<)
  #     First argument is less than the second.
  #
  #   * (<=)
-  #     First argument is less than the second.
+  #     First argument is less than or equal to the second.