Update guava prebuilt version for layoutlib tests

This is required as Change I9a987ea4 is introducing the use of guava
methods that did not exist in guava 20.0.

Bug: N/A
Test: N/A
Change-Id: I9704b3ae236c084224d09d1b0843e562a9a48d2f
(cherry picked from commit 9dc63a11483f1f3e20972dfc7c9a6aa109a76434)