Updated Pycryptodome signer to work

[GoobyCorp]

Fixes #109

[googlebot]

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[GoobyCorp]

@googlebot I signed it!

[googlebot]

CLAs look good, thanks!

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[coveralls]

Coverage decreased (-0.8%) to 42.88% when pulling a9f9fff on GoobyCorp:master into f4e597f on google:master.