Build with Java 8

Change-Id: I090ff08457fd3b149bf274a5032d2fa5bc7554a7

.buckconfig

diff --git a/.buckconfig b/.buckconfig
index dd9e0cf..f28dcad 100644
--- a/.buckconfig
+++ b/.buckconfig
@@ -5,6 +5,8 @@
 
 [java]
   src_roots = java, resources
+  source_level = 8
+  target_level = 8
 
 [project]
   ignore = .git