Synchronize protobuf with version used in rules_closure

Avoid fetching a potentially different version of protobuf-java and use
version that rules_closure transitively depends on.

Change-Id: Ief63f06cb531cd76e2bcf8c5623d653a5c1b69c7
diff --git a/lib/BUILD b/lib/BUILD
index 7fe6e10..7e4d2e8 100644
--- a/lib/BUILD
+++ b/lib/BUILD
@@ -65,7 +65,7 @@
     name = "protobuf",
     data = ["//lib:LICENSE-protobuf"],
     visibility = ["//visibility:public"],
-    exports = ["@protobuf//jar"],
+    exports = ["@com_google_protobuf//:protobuf_java"],
 )
 
 java_library(