Fix warning: Remove superfluous semicolon at namespace end.

dune/solvers/common/arithmetic.hh

@@ -588,6 +588,6 @@ namespace Arithmetic
         return OperatorHelper<OperatorType,
                               MatrixTraits<OperatorType>::isMatrix>::bmAxy(A, b, x, y);
     }
-};
+}
 
 #endif