Fix Keras to allow use with 2.1.6

[ThomasDelteil]

Hey @ilkarman there is mention of an incompatibility with keras >2.1.4, can this be fixed? I'd like to try with the keras-mxnet backend to see if there is any difference.

Thanks!

[ilkarman]

Sure I will do that tomo morning - it's mainly a change on the data-loader side