fixed warnings related to the mixed use of struct/class

src/storm/builder/ExplicitModelBuilder.h

@@ -43,7 +43,7 @@ namespace storm {
         using namespace storm::generator;
         
         // Forward-declare classes.
-        template <typename ValueType> struct RewardModelBuilder;
+        template <typename ValueType> class RewardModelBuilder;
         class ChoiceInformationBuilder;
         
         template<typename ValueType, typename RewardModelType = storm::models::sparse::StandardRewardModel<ValueType>, typename StateType = uint32_t>

src/storm/generator/Choice.cpp

@@ -174,11 +174,11 @@ namespace storm {
             return out;
         }
         
-        template class Choice<double>;
+        template struct Choice<double>;
 
 #ifdef STORM_HAVE_CARL
-        template class Choice<storm::RationalNumber>;
-        template class Choice<storm::RationalFunction>;
+        template struct Choice<storm::RationalNumber>;
+        template struct Choice<storm::RationalFunction>;
 #endif
     }
 }