Mac: Prevent admin user accidentally changing jenkins.war

Files under /Applications are usually owned by root and wheel, unless admin user has dragged it there. Jenkins is not an install-by-dragging kind of app.

osx/scripts/postinstall-war

@@ -3,5 +3,5 @@
 JENKINS_APP="/Applications/Jenkins"
 
 # Fix Jenkins Permissions
-chown -R root:admin ${JENKINS_APP}
+chown -R root:wheel ${JENKINS_APP}
 chmod -R 755 ${JENKINS_APP}