switch parent pom reference everywhere to 28 where it was 27 before
this can be safely done because the only difference between 27 and 28 is an updated maven-source-plugin (fix heap space error)

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1756968 13f79535-47bb-0310-9956-ffa450edef68
1 file changed