Update pretrained_word_embeddings example to use new API.

[yanboliang]

No description provided.

[fchollet]

?

[yanboliang]

@fchollet I think we should use embeddings_initializer to initialize weights for embedding layer, rather than set weights directly, because in the current API, no explicit argument named weights. And it also saves one assignment/initialization, as even if we set weights directly, we still need to do default initialization(embeddings_initializer='uniform'). We should encourage users to use embeddings_initializer rather than weights. If I have misunderstanding, please correct me. Thanks.

[taehoonlee]

Thank you for the PR, @yanboliang. LGTM.