message: add string tensor type mapping
diff: @@ -21,6 +21,7 @@ TENSOR_TYPE_TO_NP_TYPE = {
  TensorProto.COMPLEX128: np.dtype('complex128'),
  TensorProto.UINT32: np.dtype('uint32'),
  TensorProto.UINT64: np.dtype('uint64'),
  + TensorProto.STRING: np.dtype('str'),
  }
  NP_TYPE_TO_TENSOR_TYPE = {v: k for k, v in TENSOR_TYPE_TO_NP_TYPE.items()}
  