Fix nn notebook in docs

[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

[codecov-commenter]

Codecov Report

Merging #396 (c05b3e2) into master (4623c0e) will decrease coverage by 0.32%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #396      +/-   ##
==========================================
- Coverage   87.02%   86.70%   -0.33%     
==========================================
  Files          98       98              
  Lines        4964     4964              
==========================================
- Hits         4320     4304      -16     
- Misses        644      660      +16     

Impacted Files	Coverage Δ
etna/libs/tsfresh/distribution.py	33.33% <0.00%> (-50.01%)	⬇️
etna/libs/tsfresh/significance_tests.py	18.84% <0.00%> (-13.05%)	⬇️
etna/libs/tsfresh/relevance.py	57.14% <0.00%> (-3.81%)	⬇️

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