New versions of 3rd party packages, support for python 3.8

[MichalChromcak]

This PR covers

• an update of python 3.8 as possible version to be used
• fix of future warnings from statsmodels (including different init signature (part from fit_params moved to __init__)
• following packages updated to newer versions (see diff in environment.yaml)

prophet=1.0.1
pmdarima=1.8.1
scikit-learn=0.24
tbats=1.1.0
workalendar=15.3
pandas=1.2
numpy=1.20

[codecov-commenter]

Codecov Report

Merging #64 (a46c18d) into master (33fcf2e) will increase coverage by 0.08%. The diff coverage is 100.00%.

:exclamation: Current head a46c18d differs from pull request most recent head 25fad16. Consider uploading reports for the commit 25fad16 to get more accurate results

@@            Coverage Diff             @@
##           master      #64      +/-   ##
==========================================
+ Coverage   93.61%   93.70%   +0.08%     
==========================================
  Files          56       56              
  Lines        2633     2670      +37     
==========================================
+ Hits         2465     2502      +37     
  Misses        168      168              

Impacted Files	Coverage Δ
src/hcrystalball/model_selection/_configuration.py	96.42% <ø> (ø)
...rc/hcrystalball/model_selection/_model_selector.py	95.50% <ø> (ø)
tests/unit/test_utils.py	95.41% <ø> (ø)
...alball/feature_extraction/_seasonal_transformer.py	95.52% <100.00%> (ø)
src/hcrystalball/model_selection/__init__.py	100.00% <100.00%> (ø)
...l/model_selection/_large_scale_cross_validation.py	91.57% <100.00%> (+0.99%)	:arrow_up:
...stalball/model_selection/_model_selector_result.py	82.85% <100.00%> (+0.24%)	:arrow_up:
src/hcrystalball/wrappers/_prophet.py	94.93% <100.00%> (ø)
src/hcrystalball/wrappers/_sarimax.py	92.30% <100.00%> (ø)
tests/conftest.py	86.16% <100.00%> (ø)
... and 5 more

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[MichalChromcak]

The CI is failing on Windows for python 3.6 - the conda is unable to resolve dependencies. Removing support for python 3.6 solves the issue and I'd be up for it. What do you think @pavelkrizek ?

[pavelkrizek]

The CI is failing on Windows for python 3.6 - the conda is unable to resolve dependencies. Removing support for python 3.6 solves the issue and I'd be up for it. What do you think @pavelkrizek ?

Thanks, for updating the dependencies. I agree, let's drop support for 3.6.