set parent version to 24 and add empty relativePath where missing

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1689588 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/pom.xml b/pom.xml
index e8e1d74..157c61d 100644
--- a/pom.xml
+++ b/pom.xml
@@ -25,7 +25,8 @@
   <parent>
     <groupId>org.apache.sling</groupId>
     <artifactId>sling</artifactId>
-    <version>23</version>
+    <version>24</version>
+    <relativePath/>
   </parent>
 
   <artifactId>org.apache.sling.datasource</artifactId>