Add currency concordance for British pounds

src/MDConcCurrencies.php

@@ -34,6 +34,9 @@ final class MDConcCurrencies {
         "€" => "eu-EUR",
         "Mark (DDR)" => "ddr-Mark",
         "ddr-Mark" => "ddr-Mark",
+        "GBP" => "uk-GBP",
+        "uk-GBP" => "uk-GBP",
+        "USD" => "us-USD",
     ];
 
 }