fix computation of ETypedElement.required()

src/main/jastadd/EcoreAPI.jrag

@@ -15,7 +15,7 @@ aspect EcoreAPI {
   /**
    * abstract ETypedElement : ENamedElement ::= <Required:boolean>;
    */
-  syn boolean ETypedElement.required() = getLowerBound() != 1;
+  syn boolean ETypedElement.required() = getLowerBound() > 0;
 
   /**
    * rel EAttribute.EAttributeType -> EDataType;