Update to jekyll-sitemap v0.6.1

https://github.com/jekyll/jekyll-sitemap/releases/tag/v0.6.1
https://github.com/jekyll/jekyll-sitemap/compare/v0.6.0...v0.6.1

:chocolate_bar:
Update to jekyll-sitemap v0.6.2

Release: https://github.com/jekyll/jekyll-sitemap/releases/tag/v0.6.2
Diff since v0.6.1: https://github.com/jekyll/jekyll-sitemap/compare/v0.6.1...v0.6.2
Diff since v0.6.0: https://github.com/jekyll/jekyll-sitemap/compare/v0.6.0...v0.6.2
Bump jekyll-sitemap to v0.6.3

This release is about backwards-compatibility for versions of Jekyll before 2.5.0.
Release: https://github.com/jekyll/jekyll-sitemap/releases/tag/v0.6.3
Diff: https://github.com/jekyll/jekyll-sitemap/compare/v0.6.2...v0.6.3
Merge pull request #100 from parkr/sitemap-0.6.2

Update to jekyll-sitemap v0.6.3