Fix broken write_output method. #3

[greebie]

Fixes bug where write_output was broken. This occurred for two reasons:

1. The local parameter filename was change in the call to stdout, but not changed in the function.
2. The function referred to a no-longer-in-existence "output_write_file" function.

To test (without pypi test):

Fetch or clone repo.
cd au_notebook
pip uninstall au-notebook
python -m pip install ./

Launch notebook and test.
NOTE: The current output file request should say nb.write_output( etc.) now instead of just write_output( etc).

If for some reason, you already had the notebook running before you updated au_notebook, you will need to restart the notebook and import cells before the module will take effect.

[codecov-io]

Codecov Report

Merging #4 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master       #4   +/-   ##
=======================================
  Coverage   30.87%   30.87%           
=======================================
  Files           2        2           
  Lines         149      149           
=======================================
  Hits           46       46           
  Misses        103      103

Impacted Files	Coverage Δ
au_notebook.py	28.96% <0%> (ø)	⬆️

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[greebie]

Ha! Codecov looks like a Game of Thrones wedding. :) I'll look into a few cycles for unit testing as a way to cap this project off.