This fixes "spawn E2BIG" errors with VERY long commit messages, which
can happen with the first release after enabling semantic-release.
We should consider whether it's possible to merge multiple dependency
updates into one line, since in our situation that's the source of many
redundant lines in the changelog.
Instead of merging the configuration values in `package.json` with those
in `relase.config.js`, the `package.json` configuration was treated as
the only configuration.
