Update to parent pom 18

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1520554 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/pom.xml b/pom.xml
index 6fb1107..684238f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -21,7 +21,7 @@
     <parent>
         <groupId>org.apache.sling</groupId>
         <artifactId>sling</artifactId>
-        <version>17</version>
+        <version>18</version>
         <relativePath>../../../parent/pom.xml</relativePath>
     </parent>