Scripts: Enforce repository.directory in package.json lint script

[aduth]

Related: #13946

The wp-scripts lint-pkg-json script is used to enforce package.json standard format:

https://github.com/WordPress/gutenberg/tree/master/packages/scripts#lint-pkg-json

With the addition of repository.directory as proposed in #13946, we should also enforce the inclusion of the new field.

[aduth]

It's not clear to me whether this is supported yet in npm-package-json-lint, since this is a very new feature introduced to npm. If not, we should seek to open an issue (and/or pull request) to propose it as an enhancement.

Possibly related rules:

• https://github.com/tclindner/npm-package-json-lint/wiki/require-repository

[greatislander]

I took a stab at a PR to tclinder/npm-package-json-lint, as enforcing repository.directory is not yet supported: tclindner/npm-package-json-lint#106