add reference to boost bug

Author: pcaspers

OREAnalytics/orea/engine/historicalsensipnlcalculator.hpp

@@ -33,10 +33,10 @@
 #include <ql/shared_ptr.hpp>
 
 #include <boost/accumulators/accumulators.hpp>
-//#include <boost/accumulators/statistics.hpp>
 // Including <boost/accumulators/statistics.hpp> causes the following swig wrapper compiler errors
 //   explicit specialization of 'boost::accumulators::feature_of<boost::accumulators::tag::weighted_skewness>'
 //   explicit specialization of 'boost::accumulators::feature_of<boost::accumulators::tag::weighted_kurtosis>'
+// see https://github.com/boostorg/accumulators/issues/20
 // The following subset of includes is sufficient here and circumvents the swig errors
 #include <boost/accumulators/statistics/stats.hpp>
 #include <boost/accumulators/statistics/variance.hpp>