use Sling parent 28

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1758690 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/pom.xml b/pom.xml
index 7e456da..996b6d8 100644
--- a/pom.xml
+++ b/pom.xml
@@ -24,7 +24,7 @@
   <parent>
     <groupId>org.apache.sling</groupId>
     <artifactId>sling</artifactId>
-    <version>27-SNAPSHOT</version>
+    <version>28</version>
     <relativePath/>
   </parent>