make sure the headers module is enabled

Change-Id: Ifbb589708dc1ad818f5f1d3b25563160dbb981fd
diff --git a/roles/head-prologue/tasks/main.yml b/roles/head-prologue/tasks/main.yml
index a8b4f2b..9a5464d 100644
--- a/roles/head-prologue/tasks/main.yml
+++ b/roles/head-prologue/tasks/main.yml
@@ -25,6 +25,7 @@
     - proxy_http
     - proxy_wstunnel
     - rewrite
+    - headers
 
 - name: Enable CORD Apache Configuration
   become: yes