fix type of one hot indicators in vqvae.py
fix type of one hot indicators in vqvae.py

`tf.one_hot` defaults to `tf.float32` if no dtype is provided. This prevents `VectorQuantizerEMA` from running if its dtype is specified as `tf.float64` at init time (since the EMA tries to subtract a `tf.float32` - the one hot indicator tensor - from a `tf.float64`). This is easily fixed by passing a dtype argument to `tf.one_hot`.
deepmind/sonnet,deepmind/sonnet