RateLimiterProcessing: Adapt to older gson version

Gerrit 3.5 is using older gson version 2.8.5, without this commit: [1].
Adapt the code correspondingly. Note, that this change should be
reverted when merged up to master branch.

[1] https://github.com/google/gson/commit/c5a3f21fbad3828deba1deb88168e1f76829f807

Depends-On: https://gerrit-review.googlesource.com/c/zuul/jobs/+/339536
Change-Id: I5ae5a88fc4f48296424001732938b4ccf42e9975
1 file changed