refactor: rename lib/api to lib/registry (#1038)

lib/config/presets.js

lib/registry/docker.js

lib/registry/npm.js

lib/workers/package-file/index.js

lib/workers/package/docker.js

lib/workers/package/npm.js

test/api/docker.spec.js

test/api/npm.spec.js

test/config/presets.spec.js

test/workers/package/docker.spec.js

test/workers/package/npm.spec.js

test/workers/repository/apis.spec.js