refactor: rename clean=true to sanitize=true

lib/datasource/github.js

lib/manager/npm/extract/index.js

lib/manager/nvm/extract.js

lib/manager/travis/package.js

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

test/datasource/github.spec.js

test/manager/npm/extract/__snapshots__/index.spec.js.snap

test/manager/nvm/__snapshots__/extract.spec.js.snap