module error in unet classification - problem and fix

[VolkerH]

When pip-installing the requirements-windows.txt file, pip pulled keras version 2.2.2.

With this version, the classify-unet module will throw an error as the interface to keras.layers.merge seems to have changed recently. To fix it, one has to replace all calls of the kind keras.layers.merge([], concat_axis=3. mode='concat') to

keras.layers.merge.concatenate([e, b], axis=3).