Dockerfile: conda install libarchive

[remtav]

Description

Fixes #540

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other

How Has This Been Tested?

Docker image created locally. Successful.

Checklist:

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• My code follows the code style of this project
• I have performed a self-review of my own code
• My PR has a descriptive title
• My code follows PEP8 (most of it)
• My code have the proper documentation in the code
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new errors
• My code is covered by the existing tests (if applicable)
• [] My code includes tests that show that my feature works
• My PR passes Travis CI tests

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