fix redirects (#485)

* fix redirects

redirects seem to be broken atm, for example the https://www.swift.org/swift-compiler/ page has redirect_from: compiler-stdlib but that does not seem to work - https://www.swift.org/compiler-stdlib/ is not functional

* Update _config.yml

Author: tomerd

_config.yml

@@ -21,7 +21,7 @@ defaults:
             permalink: /blog/:title/
             layout: "post"
 
-gems:
+plugins:
   - jekyll-redirect-from
 
 whitelist: