Update Buck

java_library() now accepts provided_deps argument which replaces
use of custom java_library2() from bucklets library.

Change-Id: I3a69287543c3dbbcb5142ea77d5a6e447a073dd8

.buckversion

diff --git a/.buckversion b/.buckversion
index cec726d..2c9f529 100644
--- a/.buckversion
+++ b/.buckversion
@@ -1 +1 @@
-1ba4496a782b40dec33a42e69a74837afee06177
+021695d5e68cde7457c9849fd0a2397f91e6491e