reflect change in common from w3c/json-ld-api#638 once merged

[pchampin]

w3c/json-ld-api#638 introduces a candidate amendment in common/terms.html, which is a file shared across 3 JSON-LD specifications.

The changes should be reflected in this repo, and a change marker should be introduced it, once w3c/json-ld-api#638 is merged.