updated bc ActivitySerializer is now a typed interface

git-svn-id: https://svn.apache.org/repos/asf/incubator/streams/branches/sblackmon@1565735 13f79535-47bb-0310-9956-ffa450edef68
this file was missing from an earlier commit

git-svn-id: https://svn.apache.org/repos/asf/incubator/streams/branches/sblackmon@1565736 13f79535-47bb-0310-9956-ffa450edef68