fix XSS vector in document body issue in header.qml

Change-Id: Icb0981b2aed71f4b7e7d189eea27d5a69ef228e4
Reviewed-on: http://cr.qtquick.me/874
Tested-by: http://ci.qtquick.me/
Tested-by: R Kake <helicalgear@gmail.com>
Reviewed-by: R Kake <helicalgear@gmail.com>
Tested-by: Tasuku Suzuki <stasuku@gmail.com>
Reviewed-by: Tasuku Suzuki <stasuku@gmail.com>

contents/root/examples/header.qml

@@ -39,10 +39,10 @@ Html {
             Repeater {
                 model: http.requestHeader
                 Component {
-                    Dt { text: model.key }
+                    Dt { text: Silk.escapeHTML(model.key) }
                 }
                 Component {
-                    Dd { text: model.value }
+                    Dd { text: Silk.escapeHTML(model.value) }
                 }
             }
         }