Bump caffeine version to 2.8.0
Bump caffeine version to 2.8.0

Fixes #1602

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=311248742

cushon/error-prone,cushon/error-prone,google/error-prone,cushon/error-prone,cushon/error-prone,google/error-prone