Make record serializer accept one-dimensional arrays

[jnclt]

Issue #, if available: #320

Description of changes:
The record serializer processes reshaped arrays.
A unit test for the corresponding one-dimensional case added.

Merge Checklist

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• [x ] 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 #321 into master will decrease coverage by 0.2%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #321      +/-   ##
==========================================
- Coverage   92.92%   92.71%   -0.21%     
==========================================
  Files          50       50              
  Lines        3475     3475              
==========================================
- Hits         3229     3222       -7     
- Misses        246      253       +7

Impacted Files	Coverage Δ
src/sagemaker/amazon/common.py	97.01% <100%> (+0.74%)	⬆️
src/sagemaker/local/image.py	87.09% <0%> (-2.35%)	⬇️

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[yangaws]

The change LGTM. Just need to add an entry in the changelog.

The current version is 1.8.0. So you could add a dev version 1.8.1dev in changelog, and describe your change there following the style of changes recorded in previous versions.

[jnclt]

@yangaws , since I had made a mess of this pull request (sorry), I created a new one: #334