Update etherpad to 1.6.6

Etherpad release 1.6.6 restores the pre-1.6.4 font alignment
behavior so line numbers will match their corresponding text content
again. This is the version currently running on etherpad-dev and
exhibits no obvious regressions. Updating now also gives us over a
week to detect any new issues before the service comes under heavy
use at the Summit/Forum/OpenDev event.

Change-Id: Id3a7b4d4dd41f046658b116e4d898def2abc4ba7

modules/openstack_project/manifests/etherpad.pp

@@ -12,7 +12,7 @@ class openstack_project::etherpad (
 ) {
   class { 'etherpad_lite':
     ep_ensure      => 'latest',
-    eplite_version => '1.6.5',
+    eplite_version => '1.6.6',
     nodejs_version => '6.x',
   }