adding vega()
adding vega()

fabrice-lecuyer/QuantLib-SWIG,fabrice-lecuyer/QuantLib-SWIG,fabrice-lecuyer/QuantLib-SWIG,fabrice-lecuyer/QuantLib-SWIG,fabrice-lecuyer/QuantLib-SWIG,fabrice-lecuyer/QuantLib-SWIG,fabrice-lecuyer/QuantLib-SWIG,fabrice-lecuyer/QuantLib-SWIG,fabrice-lecuyer/QuantLib-SWIG