Update PyYAML version restriction according to requirement in docker-…

[yangaws]

…compose

Issue #, if available:

Description of changes:
https://github.com/docker/compose/blob/master/setup.py
docker-compose has this version restriction of PyYAML and we don't have the upper bound here. Our API docs https://sagemaker.readthedocs.io/en/latest/index.html then will install version 4.2b and failed to build.
So this PR made the version restriction of PyYAML consistent with docker-compose.

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[codecov-io]

Codecov Report

Merging #523 into master will decrease coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #523      +/-   ##
=========================================
- Coverage   92.82%   92.7%   -0.12%     
=========================================
  Files          71      71              
  Lines        5336    5336              
=========================================
- Hits         4953    4947       -6     
- Misses        383     389       +6

Impacted Files	Coverage Δ
src/sagemaker/local/image.py	87.76% <0%> (-1.84%)	⬇️

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