Update plugin API version to SNAPSHOT-2.6
Update plugin API version to SNAPSHOT-2.6

Also add maven-compiler-plugin to prevent the error:

   annotations are not supported in -source 1.3

Change-Id: Ic927780f0247cfbfabe3b32bdd95f2100cfb28dd

GerritCodeReview/plugins_hooks-jira,uoa-group-applications/hooks-jira,barqshasbite/its-jira