Fix: __future__ imports must occur at the beginning of the file

[IamJeffG]

This PR fixes the keras_mmist.py example script so it may be run as per this example in ClearML's docs.

Before this PR, running that example would fail with

Starting Task Execution:
  File "/root/.clearml/venvs-builds/3.10/task_repository/events.git/webinar-0620/keras_mnist.py", line 5
    from __future__ import print_function
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
SyntaxError: from __future__ imports must occur at the beginning of the file

The clearml-agent had pushed down from __future__ import print_function from line 1 to line 5, by having prefixed the following lines to the top of the script:

try: from allegroai import Task
except ImportError: from clearml import Task
(__name__ != "__main__") or Task.init()

I don't know if there's a better solution to this problem, but this one feels pretty safe as Python 2 is on its way out.

What I'm not doing: Similar modifications to scripts in the odsc20-east folder.