Update mapping_energy_with_jacobians.cpp (#1940)

Proposed by issue #1904

include/igl/mapping_energy_with_jacobians.cpp

@@ -125,7 +125,7 @@ IGL_INLINE double igl::mapping_energy_with_jacobians(
         }
         case igl::MappingEnergyType::EXP_CONFORMAL:
         {
-          energy += areas(i) * exp((pow(s1, 2) + pow(s2, 2) + pow(s3, 2)) / (3 * pow(s1 * s2 * s3, 2. / 3.)));
+          energy += areas(i) * exp(exp_factor * (pow(s1, 2) + pow(s2, 2) + pow(s3, 2)) / (3 * pow(s1 * s2 * s3, 2. / 3.)));
           break;
         }
       }