demo: Replace deprecated Granite.STYLE_CLASS_FRAME (#913)

Author: ryonakano

demo/Views/HyperTextViewGrid.vala

@@ -27,9 +27,9 @@ public class HyperTextViewGrid : DemoPage {
         var hypertext_scrolled_window = new Gtk.ScrolledWindow () {
             height_request = 300,
             width_request = 600,
-            child = hypertext_textview
+            child = hypertext_textview,
+            has_frame = true
         };
-        hypertext_scrolled_window.add_css_class (Granite.STYLE_CLASS_FRAME);
 
         var box = new Granite.Box (VERTICAL, NONE) {
             halign = CENTER,

demo/Views/WelcomeView.vala

@@ -45,7 +45,7 @@ public class WelcomeView : DemoPage {
             margin_start = 12
         };
         listbox.set_placeholder (search_placeholder);
-        listbox.add_css_class (Granite.STYLE_CLASS_FRAME);
+        listbox.add_css_class (Granite.CssClass.CARD);
 
         var search_entry = new Gtk.SearchEntry () {
             margin_top = 12,