fix issue 616

[julia-shenshina]

IMPORTANT: Please do not create a Pull Request without creating an issue first.

Before submitting (must do checklist)

• Did you read the contribution guide?
• Did you update the docs? We use Numpy format for all the methods and classes.
• Did you write any new necessary tests?
• Did you update the CHANGELOG?

Type of Change

• Examples / docs / tutorials / contributors update
• Bug fix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves an existing feature)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Proposed Changes

Related Issue

Closing issues

closes #616

[codecov-commenter]

Codecov Report

Merging #623 (b9090db) into master (0a7851d) will increase coverage by 0.05%.
The diff coverage is 93.18%.

@@            Coverage Diff             @@
##           master     #623      +/-   ##
==========================================
+ Coverage   83.96%   84.01%   +0.05%     
==========================================
  Files         118      118              
  Lines        6087     6120      +33     
==========================================
+ Hits         5111     5142      +31     
- Misses        976      978       +2     

Impacted Files	Coverage Δ
etna/models/base.py	87.73% <84.21%> (-0.27%)	⬇️
etna/models/__init__.py	100.00% <100.00%> (ø)
etna/models/catboost.py	100.00% <100.00%> (ø)
etna/models/holt_winters.py	98.82% <100.00%> (+0.04%)	⬆️
etna/models/prophet.py	98.80% <100.00%> (+0.04%)	⬆️
etna/models/sarimax.py	94.01% <100.00%> (+0.15%)	⬆️
etna/models/seasonal_ma.py	97.36% <100.00%> (+0.22%)	⬆️
etna/models/sklearn.py	94.44% <100.00%> (+0.50%)	⬆️

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