[Describe your pull request here. Please read the text below the line, and make sure you follow the checklist.]

- [ ] The changes are described in detail, both the what and why.
- [ ] If applicable, an [existing issue](https://github.com/nlohmann/json/issues) is referenced.
- [ ] The [Code coverage](https://coveralls.io/github/nlohmann/json) remained at 100%. A test case for every new line of code.
- [ ] If applicable, the [documentation](https://json.nlohmann.me) is updated.
- [ ] The source code is amalgamated by running `make amalgamate`.

Read the [Contribution Guidelines](https://github.com/nlohmann/json/blob/develop/.github/CONTRIBUTING.md) for detailed information.
