Update bazlets to the latest head of master

Most of the changes are related to Gerrit API, but it includes:

- Use bazel-cache instead of buck-cache

which is useful.

Change-Id: If951eed4c7fb517f1d8e654008816d8b2e9d8681

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index dea55d0..c5737c9 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//tools:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "6dad39cdb50b83afa7fe57783c10b272305f97ba",
+    commit = "a8bf43a97a2a655752204811d1355b180b082047",
     # local_path = "/home/<user>/projects/bazlets",
 )