Check key in collections only if it isn't "posts" (#7277)
Check key in collections only if it isn't "posts" (#7277)

Merge pull request 7277
chrisfinazzo/jekyll,tillgrallert/jekyll,Strangehill/jekyll,jaybe-jekyll/jekyll,fulldecent/jekyll,ryanshaw/jekyll,x-way/jekyll,tillgrallert/jekyll,yhironaka/yhironaka.github.io,x-way/jekyll,x-way/jekyll,jekyll/jekyll,Strangehill/jekyll,ryanshaw/jekyll,jaybe-jekyll/jekyll,ryanshaw/jekyll,Strangehill/jekyll,jaybe-jekyll/jekyll,jekyll/jekyll,chrisfinazzo/jekyll,chrisfinazzo/jekyll,tillgrallert/jekyll,tillgrallert/jekyll,x-way/jekyll,fulldecent/jekyll,fulldecent/jekyll,Strangehill/jekyll,fulldecent/jekyll,ryanshaw/jekyll,jekyll/jekyll,Strangehill/jekyll,jekyll/jekyll,chrisfinazzo/jekyll,tillgrallert/jekyll,jaybe-jekyll/jekyll