Update run_keras_server.py

[richardson-souza]

when the flask server tries to process the prediction the errors happen:
raise ValueError("Tensor %s is not an element of this graph." % obj)
ValueError: Tensor Tensor("activation 5/Sigmoid:0", shape=(?, 1), dtype=float32) is not an element of this graph.
to get around the bug a global variable graph was created.
global model, graph
model = ResNet50(weights="imagenet")
graph = tf.get_default_graph()
And with default graph predictions were made:
with graph.as_default():
preds = model.predict(image)