title: restore_best_weights issue keras early stopping
body: <p>I am using EarlyStopping from Keras for my deep learning project. The documentations <a href="https://keras.io/callbacks/#earlystopping" rel="noreferrer">here</a> mentions a very useful idea of restoring best weights. But somehow I am not able to use it yet. I am using Keras 2.2.2/TF 1.10, installed using Anaconda. 
  Call is simple as follows. is there any issue? </p>
  
  <pre><code>es = EarlyStopping(monitor='val_acc', min_delta=1e-4, patience=patience_,verbose=1,restore_best_weights=True)
  </code></pre>
  
  <blockquote>
    <p><code>__init__()</code> got an unexpected keyword argument 'restore_best_weights'</p>
  </blockquote>