fix compile error (#1955)

mobile/test/operators/test_gru_op.cpp

@@ -67,8 +67,8 @@ int TestGruOp(int in_channels, int out_channels, std::string opname) {
   auto hidden_var = scope.get()->Var("output_hidden");
 
   framework::AttributeMap attrs;
-  attrs["activation"].SetString(std::string("relu"));
-  attrs["gate_activation"].SetString(std::string("sigmoid"));
+  attrs["activation"].Set<std::string>(std::string("relu"));
+  attrs["gate_activation"].Set<std::string>(std::string("sigmoid"));
   attrs["is_reverse"].Set<bool>(false);
 
   auto *op = new operators::GruOp<CPU, float>("gru", inputs, outputs, attrs,

mobile/test/operators/test_pool_op.cpp

@@ -55,7 +55,7 @@ int TestPoolOp(int in_channels, int in_height, int in_width) {
 
   auto output_var = scope.get()->Var("output");
   framework::AttributeMap attrs;
-  attrs["pooling_type"].SetString(pooling_type);
+  attrs["pooling_type"].Set<std::string>(pooling_type);
   attrs["ksize"].Set<vector<int>>(std::vector<int>({kernel_h, kernel_w}));
   attrs["strides"].Set<vector<int>>(std::vector<int>({stride_h, stride_w}));
   attrs["paddings"].Set<vector<int>>(std::vector<int>({pad_h, pad_w}));

mobile/test/operators/test_sequence_pool_op.cpp

@@ -36,7 +36,7 @@ int TestSequencePoolOp(const framework::LoDTensor &input_x,
   auto output_var = scope.get()->Var("output");
 
   framework::AttributeMap attrs;
-  attrs["pooltype"].SetString(pool_type);
+  attrs["pooltype"].Set<std::string>(pool_type);
 
   auto *op = new operators::SequencePoolOp<CPU, float>(
       "sequence_pool", inputs, outputs, attrs, scope.get());