[MAINT] Drop 3.6 python support

[franchuterivera]

Drops support for python 3.6

[codecov]

Codecov Report

Merging #258 (8f3273b) into development (1818445) will increase coverage by 0.62%.
The diff coverage is 77.21%.

@@               Coverage Diff               @@
##           development     #258      +/-   ##
===============================================
+ Coverage        80.82%   81.44%   +0.62%     
===============================================
  Files              148      150       +2     
  Lines             8563     8566       +3     
  Branches          1323     1333      +10     
===============================================
+ Hits              6921     6977      +56     
+ Misses            1163     1108      -55     
- Partials           479      481       +2     

Impacted Files	Coverage Δ
autoPyTorch/api/tabular_regression.py	96.87% <ø> (ø)
autoPyTorch/utils/common.py	87.09% <ø> (+19.23%)	⬆️
...PyTorch/pipeline/traditional_tabular_regression.py	25.42% <25.42%> (ø)
autoPyTorch/evaluation/abstract_evaluator.py	75.89% <45.16%> (-2.28%)	⬇️
...h/pipeline/components/training/trainer/__init__.py	70.65% <50.00%> (+0.32%)	⬆️
...tup/traditional_ml/traditional_learner/learners.py	82.97% <82.97%> (ø)
...line/components/setup/traditional_ml/base_model.py	73.61% <88.88%> (+0.59%)	⬆️
...tup/traditional_ml/traditional_learner/__init__.py	91.66% <90.00%> (ø)
...ml/traditional_learner/base_traditional_learner.py	94.80% <94.80%> (ø)
.../setup/traditional_ml/tabular_traditional_model.py	96.66% <96.66%> (ø)
... and 31 more

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