Upgrade protobuf to v3.6.1

Merge commit 'be9845eb2abf508c86da76321b4e2c352b45b532' into master

Change-Id: I1b3cd2e177686afe95f44abc4fb0c6f9e001e784
diff --git a/aos/protobuf/BUILD b/aos/protobuf/BUILD
index 69c49d1..4d6a107 100644
--- a/aos/protobuf/BUILD
+++ b/aos/protobuf/BUILD
@@ -1,22 +1,22 @@
-package(default_visibility = ['//visibility:public'])
+package(default_visibility = ["//visibility:public"])
 
 cc_library(
-  name = "stack_arena",
-  srcs = ["stack_arena.cc"],
-  hdrs = ["stack_arena.h"],
-  deps = [
-    "//aos/logging:logging",
-    "//third_party/protobuf",
-  ],
+    name = "stack_arena",
+    srcs = ["stack_arena.cc"],
+    hdrs = ["stack_arena.h"],
+    deps = [
+        "//aos/logging",
+        "@com_google_protobuf//:protobuf",
+    ],
 )
 
 cc_test(
-  name = "stack_arena_test",
-  srcs = ["stack_arena_test.cc"],
-  deps = [
-    ":stack_arena",
-    "//aos/testing:test_logging",
-    "//aos/logging:logging",
-    "//aos/testing:googletest",
-  ],
+    name = "stack_arena_test",
+    srcs = ["stack_arena_test.cc"],
+    deps = [
+        ":stack_arena",
+        "//aos/logging",
+        "//aos/testing:googletest",
+        "//aos/testing:test_logging",
+    ],
 )