test: fix coverage (#3794)

.tslintrc.js

lib/datasource/docker/index.js

lib/manager/composer/artifacts.js

lib/manager/gomod/artifacts.js

lib/manager/npm/extract/monorepo.js

lib/manager/npm/post-update/yarn.js

lib/manager/pip_setup/extract.js

lib/platform/github/index.js

lib/platform/github/storage.js

lib/workers/branch/index.js

lib/workers/global/index.js

lib/workers/pr/changelog/source-github.js

lib/workers/repository/finalise/validate.js

lib/workers/repository/process/lookup/index.js

lib/workers/repository/updates/generate.js

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

test/config/presets.spec.js

test/datasource/__snapshots__/docker.spec.js.snap

test/datasource/docker.spec.js

test/datasource/github.spec.js