This release includes a memory leak fix, and a fix for removing reducers with replaceReducer and combineReducers.
There are also some TypeScript changes, which require version 3.5 or higher. This also removes our DeepPartial type, which wasn't intended to be a public API. If you need this type, you can find an equivalent of likely higher quality in the utility-types package.
Speaking of TypeScript, we are done with converting the code to TypeScript on master and are looking to get some TS improvements in before launching 5.0. If you're interested in helping, feel free to submit a PR with anything you'd like to contribute.