to trigger ci for multiplex_op

Author: Yibing Liu

paddle/operators/multiplex_op.cc

@@ -94,7 +94,7 @@ class MultiplexGradOp : public framework::OperatorWithKernel {
     PADDLE_ENFORCE(!ctx.MultiOutputVar(framework::GradVarName("X")).empty(),
                    "Output(X@Grad) should not be null.");
     PADDLE_ENFORCE_NOT_NULL(ctx.InputVar(framework::GradVarName("Out")),
-                            "Input(Out@GRAD) shouldn't be null.");
+                            "Input(Out@GRAD) should not be null.");
     auto d_ins = ctx.MultiOutput<Tensor>(framework::GradVarName("X"));
     auto ins = ctx.MultiInput<Tensor>("X");
     // No need to compute gradient for Input(Ids)