Fix issue with deeply nested build sitemap build dirs when publishing docs

[fgrehm]

https://github.com/doximity/vital/commit/45648e6abcecdb6ce4c76ecd51e2c4e8b8c54156#diff-5d33eb6e08d0e909877a35911fee9f7cL1

Looks like every time we run bundle exec middleman build --clean on the docs/ dir it generates a nested build dir under it, not sure why yet