bug in sparse_categorical_crossentropy in theano backend

[udibr]

theano sparse_categorical_crossentropy calls categorical_crossentropy on line
https://github.com/fchollet/keras/blob/master/keras/backend/theano_backend.py#L1539
but the call is using the wrong order of parameters. should be

    return categorical_crossentropy(target, output, from_logits)

[stale]

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