Fixed comment to refer to the right int accessor for Quantity

It's AsInt64() not Int64().

Author: Ihar Hrachyshka

api/openapi-spec/swagger.json

@@ -29,7 +29,7 @@ import (
 
 // Quantity is a fixed-point representation of a number.
 // It provides convenient marshaling/unmarshaling in JSON and YAML,
-// in addition to String() and Int64() accessors.
+// in addition to String() and AsInt64() accessors.
 //
 // The serialization format is:
 //