FFI gem ver >= 13 cannot load proj

[isaacrowntree]

To reproduce try

require 'proj'

Run the file. FFI versions greater than 12 throw an error related to these changes in the FFI gem:

Changelog for version 1.13.0:

Reject callback with :string return type at definition, because it didn't work so far and is not save to use. #751, #782

Links to issues:

ffi/ffi#751
ffi/ffi#782

[cfis]

Hmm, ok. Do you know what callback is causing the error? Want to submit a patch?

[cuirc]

Looks like it's triggered by proj_file_finder