feat: use purl for nvm

lib/manager/_helpers/node/package.js

lib/manager/nvm/extract.js

lib/manager/nvm/index.js

lib/manager/nvm/package.js

test/manager/_helpers/node/package.spec.js

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

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

test/manager/nvm/package.spec.js