roles/nginx: Enable SPDY header compression

Recommended by Ilya Grigorik to be set to 6.

Signed-off-by: Alan Orth <alan.orth@gmail.com>

roles/nginx/templates/https.j2

@@ -23,6 +23,9 @@
     # of such infrastructure, consider turning off session tickets:
     ssl_session_tickets off;
 
+    # enable SPDY header compression
+    spdy_headers_comp 6;
+
     # Enable this if you want HSTS (recommended, but be careful)
     add_header Strict-Transport-Security max-age=15768000;