core key is now necessary in .info.yml files

Due to a recent change in Drupal.org packaging, #3075062: Remove core key overriding in .info.yml packaging, a change is needed in your project.

The relatedbyterms.info.yml file in your project needs a line like:

core: 8.x

If this is not added, future releases of your project will not be able to run with Drupal.