added referrer meta tag

Author: guardofparadise

src/index.html

@@ -4,6 +4,7 @@
   <meta charset="utf-8">
   <title>Angular Material Admin Full</title>
   <base href="./">
+  <meta name="referrer" content="no-referrer-when-downgrade">
   <meta name="description" content="Open-Source admin template built with Angular based on Angular Material.">
   <meta name="keywords" content="angular material admin, angular material dashboard, angular material, material template, angular template.">
   <meta name="author" content="Flatlogic LLC">