Log Message:
devel/ruby-ffi: update to 1.13.1

Update ruby-ffi to 1.13.1.

1.13.1 / 2020-06-09
-------------------

Changed:
* Revert use of `ucrtbase.dll` as default C library on Windows-MINGW.
  `ucrtbase.dll` is still used on MSWIN target. #790
* Test for `ffi_prep_closure_loc()` to make sure we can use this function.
  This fixes incorrect use of system libffi on MacOS Mojave (10.14). #787
* Update types.conf on x86_64-dragonflybsd