Bump pom.xml to Gerrit-2.8.1, added plugin repository Bump the pom.xml version to 2.8.1 to match released version of Gerrit. Added https://gerrit-api.commondatastorage.googleapis.com/release to repositories section to ensure latest plugin API is available. Change-Id: I7a5d7533a6ffadb2ff28ede1cdf4fc61c0b1cff7