Fix when no expressions or keep_warm is false

[manycoding]

When I set keep_warm_expression it fails with

    events=events
  File "/Users/valery/.local/share/virtualenvs/document_data_extract_zappa-j8vc3Vbe/lib/python3.6/site-packages/zappa/core.py", line 2783, in schedule_events
    print("Could not create event {} - Please define either an expression or an event source".format(name))
UnboundLocalError: local variable 'name' referenced before assignment

So I fixed it.

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GitHub Issues

[coveralls]

Coverage decreased (-0.02%) to 72.954% when pulling 6aabdf416e3883bd133bf9dd54aaa32778972f12 on manycoding:patch-1 into 542c8c60291ebc5ece03b8dd4abe9e0172715086 on Miserlou:master.