Bump version to 1.15.1

[jesterhazy]

Description of changes:

• increment version

Merge Checklist

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• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works (if appropriate)
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[codecov-io]

Codecov Report

Merging #506 into master will increase coverage by 0.12%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #506      +/-   ##
==========================================
+ Coverage   94.13%   94.26%   +0.12%     
==========================================
  Files          59       59              
  Lines        4621     4621              
==========================================
+ Hits         4350     4356       +6     
+ Misses        271      265       -6

Impacted Files	Coverage Δ
src/sagemaker/__init__.py	100% <100%> (ø)	⬆️
src/sagemaker/local/image.py	89.6% <0%> (+1.83%)	⬆️

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