Fix outdated `literate.jl` script

[devmotion]

This PR fixes some outdated stuff in the literate.jl, independently of the other PRs concerning examples/Literate/Documenter:

• The nothing #hide bug was fixed in https://github.com/fredrikekre/Literate.jl/pull/188
• documenter=... is deprecated, instead one should specify the Markdown flavour. Since for Markdown the default is DocumenterFlavour, I removed the keyword argument
• documenter=... is ignored for notebook output, so I removed the keyword argument there as well

[codecov[bot]]

Codecov Report

Merging #111 (1520111) into master (bae0a1e) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #111   +/-   ##
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  Coverage   95.78%   95.78%           
=======================================
  Files           4        4           
  Lines         285      285           
=======================================
  Hits          273      273           
  Misses         12       12           

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