Build with Java 8

Change-Id: Ia72235afb7f3a258757d610a9ca63c17aebc6415

.buckconfig

diff --git a/.buckconfig b/.buckconfig
index 7ab2a74..36cf847 100644
--- a/.buckconfig
+++ b/.buckconfig
@@ -10,6 +10,8 @@
 
 [java]
   src_roots = java, resources
+  source_level = 8
+  target_level = 8
 
 [project]
   ignore = .git