License plugin header missing

The WordPress.org plugin page has a message for logged in committers:

> The `License` field is missing. [A GPLv2 or later compatible license](https://www.gnu.org/licenses/license-list.en.html) should be specified.

Possibly related to the changes highlighted at https://github.com/Automattic/Edit-Flow/commit/7b8f449aaca24e142e9333d204606776bd39a7df.