Bump to jekyll-redirect-from v0.6.2

  Fix for if `site.github` isn't a `Hash` when trying to access `site.github.url`.

Only affects those who have set `github` in their site `_config.yml`'s but it will cause build failures galore.

*Veeery small diff*: https://github.com/jekyll/jekyll-redirect-from/compare/v0.6.0...v0.6.1

Release: https://github.com/jekyll/jekyll-redirect-from/releases/tag/v0.6.1

Release numero dos: https://github.com/jekyll/jekyll-redirect-from/releases/tag/v0.6.2

/cc @kansaichris @mastahyeti @benbalter