message: Re-order member variable in ProductionCost class
  This fixes the warning about the constructor member initializer list not
  matching the order of member variables.
diff: @@ -37,9 +37,9 @@ public:
  int turnsToBuild() const { return mTurnsToBuild; }
  private:
  + int mTurnsToBuild = 0;
  int mCommonMetals = 0;
  int mCommonMinerals = 0;
  int mRareMetals = 0;
  int mRareMinerals = 0;
  - int mTurnsToBuild = 0;
  };
  