Use json get_ref

[apivovarov]

Niels Lohmann recommends to use json.get_ref() instead of json.get() in case we use json object as a shared read-only storage of strings.

nlohmann/json#2130

Testing

model_peeker

# bin/model_peeker ../tests/python/integration/resnet18_v1
[07:40:46] /root/workplace/neo-ai-dlr/src/dlr_tvm.cc:68: Loading metadata file: ../tests/python/integration/resnet18_v1/resnet18.meta
backend is tvm
num_inputs = 1
num_weights = 62
num_outputs = 1
input_names: data,
input_types: float32,
output shapes:
[1, 1000, ]
output_names: softmax_tensor (index: 0),
output_types: float32,

run_resnet

# bin/run_resnet ../tests/python/integration/resnet18_v1 ~/workplace/models/dog_float32.npy
Loading model...
[07:41:08] /root/workplace/neo-ai-dlr/src/dlr_tvm.cc:68: Loading metadata file: ../tests/python/integration/resnet18_v1/resnet18.meta
Running inference...
Max probability is 0.994058 at index 151