Fix 2 warnings by not using deprecated Keras API
Fix 2 warnings by not using deprecated Keras API

Fixes 2 warnings:

example.py:58: UserWarning: The `merge` function is deprecated and will be removed after 08/2017. Use instead layers from `keras.layers.merge`, e.g. `add`, `concatenate`, etc.
  x = merge([action_input, flattened_observation], mode='concat')
/home/adam/anaconda2/envs/opensim-rl/lib/python2.7/site-packages/keras/legacy/layers.py:456: UserWarning: The `Merge` layer is deprecated and will be removed after 08/2017. Use instead layers from `keras.layers.merge`, e.g. `add`, `concatenate`, etc.
  name=name)

example.py:67: UserWarning: Update your `Model` call to the Keras 2 API: `Model(outputs=Tensor("de..., inputs=[<tf.Tenso...)`
  critic = Model(input=[action_input, observation_input], output=x)

stanfordnmbl/osim-rl,vzhuang/osim-rl