Use latest parent

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1616689 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/pom.xml b/pom.xml
index a6c191f..b728002 100644
--- a/pom.xml
+++ b/pom.xml
@@ -26,7 +26,7 @@
     <parent>
         <groupId>org.apache.sling</groupId>
         <artifactId>sling</artifactId>
-        <version>19</version>
+        <version>20</version>
     </parent>
 
     <modelVersion>4.0.0</modelVersion>