www: Change de-AT to de

www/de/index.xhtml

@@ -21,7 +21,7 @@
   <meta property="og:image:type" content="image/jpeg"/>
   <meta property="og:image:width" content="1200"/>
   <meta property="og:image:height" content="630"/>
-  <meta property="og:locale" content="de_AT"/>
+  <meta property="og:locale" content="de"/>
   <meta property="og:ttl" content="60"/>
   <meta name="twitter:card" content="summary_large_image"/>
 </head>