Delete old plugin folder when upgrading to 1.1.0

[khalwat]

Just a note here for people of an issue someone just ran into.

When upgrading to SEOmatic 1.1.0, make sure that you delete the old seomatic folder before you do the upgrade.

Some FTP clients, and I think Windows, will do a merge by default, which will cause SEOmatic 1.1.0 to not function properly, because I renamed a bunch of files from xxxx.html to xxxx.twig, and a merge copy will keep them both in place.