fix unclosed version file warning

[demianbrecht]

Fixes

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the development branch.
• [] I have added tests that prove my fix is effective or that my feature works
• [] I have added necessary documentation about the functionality in the appropriate .md file
• [] I have added in line documentation to the code I modified

Short description of what this PR does:

Tiny fix that removes the following unclosed file warning:

python -Wd -m unittest discover -v
/src/spython-http-client/python_http_client/__init__.py:22: ResourceWarning: unclosed file <_io.TextIOWrapper name='/src/python-http-client/python_http_client/VERSION.txt' mode='r' encoding='UTF-8'>
  __version__ = open(os.path.join(dir_path, 'VERSION.txt')).read().strip()

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[childish-sambino]

Duplicates #128