Fixed updateThreadsStatus to modify original thread instances, rather than modifying copies

[jishi9]

This is a proposed fix to #22

updateThreadsStatus was not actually updating the CommentThread instances, but updating copies thereof.

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[jishi9]

I signed it!

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We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for the commit author(s). If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.

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CLAs look good, thanks!

[ojarjur]

Thanks for doing this; good catch on the bug.