What does this PR do?

Currently Crawler does not let JavaScript run on crawled pages. This leads to issues for websites that rely on fully dynamically loaded content that is not present in the DOM at loading time, but is fetched with JS immediately after.

We should investigate how to allow JavaScript to run on the crawled pages with Selenium and add a switch to the Crawler that allows users to do this.

Based on

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https://github.com/PaddlePaddle/PaddleNLP/tree/develop/examples/machine_translation/transformer
在我们的基于 Transformer 的 Machine Translation 例子中，数据准备这一步奏仅提供了

From paper, it mentioned

Instead, the training data generator chooses 15% of tokens at random, e.g., in the sentence my
dog is hairy it chooses hairy.

It means that 15% of token will be choose for sure.

From https://github.com/codertimo/BERT-pytorch/blob/master/bert_pytorch/dataset/dataset.py#L68,
for every single token, it has 15% of chance that go though the followup procedure.