fix: do not log InvalidDocumentException as an uncaught error

[keetonian]

Issue #, if available:
N/A
Description of changes:
InvalidDocumentExceptions were being logged as uncaught exceptions. This removes this unnecessary logging.
Description of how you validated changes:
make pr ran and passed. Travis is running.
Checklist:

• Write/update tests
• make pr passes
• Update documentation
• Verify transformed template deploys and application functions as expected
• Add/update example to examples/2016-10-31

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #973 into develop will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           develop    #973   +/-   ##
=======================================
  Coverage     94.8%   94.8%           
=======================================
  Files           69      69           
  Lines         3079    3079           
  Branches       580     580           
=======================================
  Hits          2919    2919           
  Misses          84      84           
  Partials        76      76

Impacted Files	Coverage Δ
samtranslator/plugins/__init__.py	100% <100%> (ø)	⬆️

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