changed "when" statement

if using '{{}}’, you need to quote the whole line

roles/webserver/tasks/main.yml

@@ -7,6 +7,6 @@
       msg: Debug
   # install software
   - import_tasks: install_apache.yml
-    when: "{{ apache }}" is true
+    when: "{{ apache }} == true"
   - import_tasks: install_nginx.yml
-    when: "{{ nginx }}" is true
+    when: "{{ nginx }} == true"