Cleanup _config.yml

Just a few things I noticed in `_config.yml`. Assuming this was inspired by another site, so pointing out in case the settings weren't intentional.

> `safe: true`

Safe mode disabled plugins (this repo doesn't have any)

> `auto: true`

Deprecated, use `--watch` flag at runtime

> `source: api-evangelist`
> `destination: api-evangelist`

This would override the build source and destination when built locally, resulting in the build failing. By default, this is `./` and `_site`. Is there are reason you'd want it elsewhere (much less the same)?

> `exclude: [".rvmrc", ".rbenv-version", "README.md", "Rakefile", "changelog.md"]`

None of these files exist in the repo. Safe to remove or modify.