fix ReduceMean.hpp initializer_list as vector

include/aidge/operator/ReduceMean.hpp

@@ -96,7 +96,7 @@ class ReduceMean_Op : public OperatorTensor,
                     outDims.erase(outDims.begin() + static_cast<std::size_t>(*it));
             }
 
-            mOutputs[0]->resize((outDims.size()>0) ? outDims : {1});
+            mOutputs[0]->resize((outDims.size()>0) ? outDims : std::vector<DimSize_t>({1}));
 
         }
     }