Document's struct fields missing "statements" field in OPENVEX-SPEC.md

[colin-pm]

In OPENVEX-SPEC.md, I noticed that the table listing fields for the Document struct is missing a row for the "statements" field. The "statements" field is included in the minimal example above the table.

https://github.com/openvex/spec/blob/main/OPENVEX-SPEC.md#document-struct-fields