fixed tf 2.2.0 weight error

[pyu10055]

In TF 2.2.0 the recurrent network weight name has been changed, now it is in
form of layer_name/cell_name/weight_name
We need to be able to handle both TF 2.1.0 format layer_name/weight_name and
2.2.0 format

Fixed #3314

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This change is 

[lina128]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @lina128 and @pyu10055)

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tfjs-converter/python/tensorflowjs/converters/keras_tfjs_loader.py, line 92 at r1 (raw file):

        # the inner cell name.
        tokens = name.split('/')
        shorten_name = '/'.join(name[0:-2] + [name[-1]])

'/'.join(tokens[0:-2] + [tokens[-1]])

[pyu10055]

Reviewable status: complete! 1 of 1 approvals obtained

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tfjs-converter/python/tensorflowjs/converters/keras_tfjs_loader.py, line 92 at r1 (raw file):

Previously, lina128 (Na Li) wrote…

'/'.join(tokens[0:-2] + [name[-1]])

Done.