Remove deprecated dependency jekyll-algolia

[alouiadel]

This is a documentation change.

Summary

Removed mentioning of now deprecated jekyll-algolia gem from documentation
i also suggest you check : mmistakes/mm-github-pages-starter#59

Context

Is this related to any GitHub issue(s)?
No, i had to setup my personal website using this template , this is how i encountered this.

[iBug]

Algolia is still one of the best search providers out there. If you remove jekyll-algolia, consider documenting its successor gem instead.

[alouiadel]

It seems that no alternative gem is available since Jekyll isn't popular enough to encourage API providers to create these gems. However, I view keeping a deprecated gem active as a vulnerability and a security concern for the template users

[iBug]

Since Algolia integration remains a stood-out feature of the theme, I prefer keeping the documentation or one of its substitutes in place, until the status quo stops working altogether.

Also, I don't consider a deprecated gem "a vulnerability" in a static site generator until proven to be dangerous. Deprecation only means it'll stop being maintained, not being taken over by hostile parties.

[alouiadel]

ok fair enough