Examples does not work with apex optimizers
Under fp16 option, optimizer is replaced by one from apex, which does not have the attribute ```get_lr()``` .

https://github.com/huggingface/pytorch-pretrained-BERT/blob/98dc30b21e3df6528d0dd17f0910ffea12bc0f33/examples/run_squad.py#L315-L317

Should be able to reproduce the error by running the example [here](https://github.com/huggingface/pytorch-pretrained-BERT#fine-tuning-bert-large-on-gpus) in the README, error message should be something like ```AttributeError, FP16_Optimizer does not have attribute get_lr()```
You can  use #  on line 316 and it can solved this problem.