Update LICENSE.md for new fast-json-stable-stringify.

As of #2065, we no longer
use `json-stable-stringify`, which pulled in `jsonify` — a dependency which
is licensed under a public-domain license which is not agreeable with some
organizations.  The `fast-json-stable-stringify` license does not rely on
`jsonify`.

This swaps the package being licensed, but the license itself is the same
(MIT).

packages/apollo-server-plugin-operation-registry/LICENSE.md

@@ -3,7 +3,7 @@ Copyright (c) 2018- Meteor Development Group, Inc.
 The following sets forth attribution notices for third party software that may
 be contained in portions of this package.
 
-### `json-stable-stringify`
+### `fast-json-stable-stringify`
 
 ```
 This software is released under the MIT license: