refactor: separateMajorReleases -> separateMajorMinor

docs/design-decisions.md

lib/config/definitions.js

lib/config/migration.js

lib/manager/docker/package.js

lib/manager/npm/versions.js

test/_fixtures/npm/renovate-config-default.json

test/_fixtures/npm/renovate-config-ikatyang.json

test/config/__snapshots__/index.spec.js.snap

test/config/__snapshots__/migration.spec.js.snap

test/config/__snapshots__/presets.spec.js.snap

test/config/migration.spec.js

test/manager/npm/versions.spec.js

website/docs/configuration-options.md

website/docs/faq.md