add redirects for 8.0 (#10)

Author: terakilobyte

config/redirects

@@ -3,7 +3,7 @@ define: base https://www.mongodb.com/docs/mongoid
 define: master https://www.mongodb.com/docs/mongoid/master
 
 symlink: upcoming -> master
-symlink: current -> 7.4
+symlink: current -> 8.0
 
 raw: ${prefix}/ -> ${base}/current/
 raw: ${prefix}/upcoming -> ${master}/