Update tflite schema version to 1.13

[apivovarov]

In order to parse tflite flatbuffers files tflite frontend needs tensorflow/lite/schema/schema.fbs
Currently we use schema from version r1.12

when we run pip3 install tensorflow in Ubuntu 16.04 docker container pip3 installs tensorflow 1.13.1.
Better to update tflite schema to r1.13 as well

lite module was moved from tensorflow/contrib/ to just tensorflow/ in version 1.13
This PR changes

1. update schema.fbs version to r1.13
2. updates lite module location (drops "contrib")

[apivovarov]

@FrozenGene Can you have a look?

[tqchen]

Thanks, @FrozenGene @apivovarov , this PR is now merged

[apivovarov]

@tqchen looks like Jenkins workers still uses tflite package v1.12
Can you look at the issue - #3373

[wangshangsam]

I just want to point out that, in the same file you changed (tests/python/frontend/tflite/test_forward.py) but a few lines after that, there's another "tf.contrib.lite":

def compare_tflite_with_tvm(in_data, in_name, input_tensors,
                            output_tensors, init_global_variables=False):
    """Generic function to generate and compare TFLite and TVM output"""
    in_data = convert_to_list(in_data)
    in_name = convert_to_list(in_name)
    in_node = [0] * len(in_name)
    for i in range(len(in_name)):
        in_node[i] = in_name[i].split(':')[0] if ":" in in_name[i] else in_name[i]

    with tf.Session() as sess:
        if init_global_variables:
            sess.run(variables.global_variables_initializer())
        # convert to tflite model
        converter = tf.contrib.lite.TFLiteConverter.from_session(
            sess, input_tensors, output_tensors)
        tflite_model_buffer = converter.convert()
        tflite_output = run_tflite_graph(tflite_model_buffer, in_data)

        for device in ["llvm"]:
            ctx = tvm.context(device, 0)
            if not ctx.exist:
                print("Skip because %s is not enabled" % device)
                continue

            tvm_output = run_tvm_graph(tflite_model_buffer, in_data, in_node, target=device)
            for i in range(len(tflite_output)):
                tvm.testing.assert_allclose(tflite_output[i], tvm_output[i], atol=1e-5, rtol=1e-5)

I'm just amazed by how the CI tests after this PR were even passing to begin with ......

[FrozenGene]

@apivovarov Could you help to resolve @wangshangsam 's question?