test: fix issue with former Eigen version

unittest/complex.cpp

@@ -56,7 +56,7 @@ Eigen::Matrix<std::complex<Scalar>,Rows,Cols,Options>
 ascomplex(const Eigen::Matrix<Scalar,Rows,Cols,Options> & mat)
 {
   typedef Eigen::Matrix<std::complex<Scalar>,Rows,Cols,Options> ReturnType;
-  return ReturnType(mat);
+  return ReturnType(mat.template cast<std::complex<Scalar> >());
 }
 
 BOOST_PYTHON_MODULE(complex)