undefined issues

Hi, just trying to write a nice tool for angular, utilizing your tool angular-pouchdb.
I see, in the doc of pouchdb, that there should be a replicate pointer to PouchDB.replicate on each instance ... when running I get errors ... with 2.1.0 and the current 2.2.3 as well ...
This lil fix should workaround this issue (same goes for sync/destroy)