refactor: rename some versioning interface (#2078)

lib/datasource/github.js

lib/manager/buildkite/extract.js

lib/manager/nvm/extract.js

lib/manager/pip_requirements/package.js

lib/manager/travis/package.js

lib/versioning/pep440/index.js

lib/versioning/pep440/range.js

lib/versioning/semver/index.js

lib/versioning/semver/range.js

lib/workers/pr/changelog/manager-pip.js

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

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

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

test/versioning/semver.spec.js