Upgrade protobuf-java to 3.4.0 (redux)

The original upgrade was reverted so we can release gitiles
without it. Redo it after the version bump.

Change-Id: Ie05af578362aed7e9b90bd06d7da3a759d3735c2

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 7c4b386..d507f25 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -116,8 +116,8 @@
 
 maven_jar(
     name = "protobuf",
-    artifact = "com.google.protobuf:protobuf-java:3.0.0-beta-2",
-    sha1 = "de80fe047052445869b96f6def6baca7182c95af",
+    artifact = "com.google.protobuf:protobuf-java:3.4.0",
+    sha1 = "b32aba0cbe737a4ca953f71688725972e3ee927c",
 )
 
 maven_jar(