Rename tokenExpiry field to prevent Folder corruption issues when upgrading from old versions of this plugin

[dwnusbaum]

XStream attempts to deserialize all fields in XML files that have a corresponding field in the class, even if it is marked transient. This means that #325 did not actually fix the issues described in #323, #324, and #326, which were caused by #223.

This should fix #323, #324, and #326. I tested it manually with a corrupted folder.

Testing done

Submitter checklist

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• [x] Ensure that the pull request title represents the desired changelog entry
• [x] Please describe what you did
• [x] Link to relevant issues in GitHub or Jira
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• [ ] Ensure you have provided tests - that demonstrates feature works or fixes the issue

[bluesliverx]

I'm not sure who has merge permissions here, but I do not.

[dwnusbaum]

@jetersen Any chance you can help get this released?