chore: don't generate javadoc (#18)

The javadoc generation fails with multiple errors and we don't need to generate it
for these tests.
diff --git a/pom.xml b/pom.xml
index e3c2fb8..86e5e44 100644
--- a/pom.xml
+++ b/pom.xml
@@ -59,6 +59,8 @@
     <launchpad.readiness.mediatype>.txt:text/plain</launchpad.readiness.mediatype>
 
     <jackrabbit.version>2.16.3</jackrabbit.version>
+
+    <javadoc.excludePackageNames>org.apache.sling.*</javadoc.excludePackageNames>
   </properties>
 
   <scm>