[#30] Documents: Add WineQualityStatistics

Elwig/Documents/Document.cs

@@ -86,6 +86,8 @@ namespace Elwig.Documents {
                 name = "MemberDataSheet";
             } else if (this is MemberList) {
                 name = "MemberList";
+            } else if (this is WineQualityStatistics) {
+                name = "WineQualityStatistics";
             } else {
                 throw new InvalidOperationException("Invalid document object");
             }