Adding missing executable bit to presentations/gerrit-new-features-2.6/makeslides file

Change-Id: Ie975b65ea054326587728812f86eca1bab893ac2
diff --git a/presentations/gerrit-new-features-2.6/makeslides b/presentations/gerrit-new-features-2.6/makeslides
old mode 100644
new mode 100755