Set transport options on requests session

[ThatIsGeek]

Fix for #20

[codecov-io]

Codecov Report

Merging #21 into master will decrease coverage by 1.73%. The diff coverage is 0%.

@@            Coverage Diff            @@
##           master     #21      +/-   ##
=========================================
- Coverage   89.03%   87.3%   -1.74%     
=========================================
  Files           7       7              
  Lines         310     315       +5     
  Branches       30      33       +3     
=========================================
- Hits          276     275       -1     
- Misses         22      25       +3     
- Partials       12      15       +3

Impacted Files	Coverage Δ
etcd3gw/client.py	85.06% <0%> (-3.53%)	:arrow_down:

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[dims]

Thanks @ThatIsGeek !