Merge pull request #100 from JanxSpirit/master

more descriptive exception message than MatchError

src/main/scala/com/wordnik/swagger/model/SwaggerModelSerializer.scala

@@ -87,6 +87,7 @@ object SwaggerSerializers {
           new ResourceListingSerializer +
           new ApiListingSerializer
       }
+      case _ => throw new IllegalArgumentException("%s is not a valid Swagger version".format(version))
     }
   }