* Max Over Time in imdb_cnn.py
Following this issue https://github.com/fchollet/keras/issues/2296 i propose this PR.
The mayor optimisation a part of the Max over time are:
- Dropout in the Embedding layer.
- Longer input sequences (400 instead of 100), made possible from the speedup of the Max Over Time.
- Adam optimizer.
Overall it takes 90 to 100 sec per epoch on my laptop CPU and in two epochs it reaches 0.885 accuracy that is a 5 points improvement over the previous implementation. Moreover it requires less memory (300k parameters vs 3M+) since the number of parameters do not depend by the length of the input sequence anymore.
* Update imdb_cnn.py
