Update changelog history links

Author: laurentpellegrino

CHANGELOG.md

@@ -56,7 +56,8 @@ https://github.com/ipregistry/ipregistry-python#caching
 ## [1.0.0] - 2019-07-28
 - First public release.
 
-[Unreleased]: https://github.com/ipregistry/ipregistry-javascript/compare/3.2.0...HEAD
+[Unreleased]: https://github.com/ipregistry/ipregistry-javascript/compare/4.0.0...HEAD
+[4.0.0]: https://github.com/ipregistry/ipregistry-javascript/releases/tag/3.2.0...4.0.0s
 [3.2.0]: https://github.com/ipregistry/ipregistry-javascript/releases/tag/3.1.0...3.2.0
 [3.1.0]: https://github.com/ipregistry/ipregistry-javascript/releases/tag/3.0.0...3.1.0
 [3.0.0]: https://github.com/ipregistry/ipregistry-javascript/releases/tag/2.0.1...3.0.0