Link API docs to master

Author: p

source/index.txt

@@ -29,7 +29,7 @@ for MongoDB in Ruby.
    /tutorials/mongoid-transactions
    /tutorials/mongoid-rails
    /tutorials/mongoid-upgrade
-   API <https://docs.mongodb.com/mongoid/7.0/api/>
+   API <https://docs.mongodb.com/mongoid/master/api/>
 
 
 For documentation on Mongoid 3 and 4, see `<http://mongoid.github.io>`_.