Upgrade guava to 21.0

Change-Id: I784829f563e86f4df90b63d82e43c1df38aa5e8c

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 75f5759..fb85d72 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -22,8 +22,8 @@
 
 maven_jar(
     name = "guava",
-    artifact = "com.google.guava:guava:19.0",
-    sha1 = "6ce200f6b23222af3d8abb6b6459e6c44f4bb0e9",
+    artifact = "com.google.guava:guava:21.0",
+    sha1 = "3a3d111be1be1b745edfa7d91678a12d7ed38709",
 )
 
 maven_jar(