This fixes a few whitespace issues. In doing so, it changes the serialisation to end with a single newline instead of two, which was causing occasional whitespace-check errors.

Checklist

• I have read the contribution guidelines.
• I have updated the documentation, if applicable.
• I have tested my change(s) in the test suite, and added new test cases where necessary.
• My code follows the Gaffer project's prevailing coding style and conventions.