Add parameter `allow_pickle = True` to common.utils.process_imdb()

[lebensterben]

When processing the IMDB data for RNN, I got an error which suggests to allow pickle.

I found the following fix works for me:

• In common/utils.py, change line 177 to with np.load('imdb.npz', allow_pickle = True) as f: from with np.load('imdb.npz') as f: