Fix None/True/False handling in Arango.

[tillahoffmann]

Minor changes to let None default to environment variables and True/False to be used as is. Cf. #221.

[codecov-commenter]

Codecov Report

Merging #222 (3f720fa) into master (c0dc701) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #222      +/-   ##
==========================================
+ Coverage   86.52%   86.56%   +0.03%     
==========================================
  Files          27       27              
  Lines         720      722       +2     
  Branches       65       65              
==========================================
+ Hits          623      625       +2     
  Misses         76       76              
  Partials       21       21              

Impacted Files	Coverage Δ
testcontainers/arangodb.py	100.00% <100.00%> (ø)

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[nshine]

Hi @tillahoffmann / @thedrow / @SergeyPirogov
Can you please trigger new release ?

[tillahoffmann]

@nshine, that should already be done. Let me know if you have a problem installing 3.6.0.