Bump version of Caffeine to 2.3.4
Bump version of Caffeine to 2.3.4

Problem

Recently we upgraded Caffeine to 2.3.3 just missing the release of
version 2.3.4 [1].

Solution

Upgrade to version 2.3.4.

[1] https://github.com/twitter/finagle/commit/e321b8efb6df955e495a968e1a766ff61630fe4c#commitcomment-19640764

RB_ID=886770

BuoyantIO/twitter-util,twitter/util,twitter/util,BuoyantIO/twitter-util,BuoyantIO/twitter-util,twitter/util,BuoyantIO/twitter-util