Update sanity test to validate protobuf 3.5.2

tools/run_tests/sanity/check_submodules.sh

@@ -31,7 +31,7 @@ cat << EOF | awk '{ print $1 }' | sort > "$want_submodules"
  886e7d75368e3f4fab3f4d0d3584e4abfc557755 third_party/boringssl-with-bazel (version_for_cocoapods_7.0-857-g886e7d7)
  30dbc81fb5ffdc98ea9b14b1918bfe4e8779b26e third_party/gflags (v2.2.0)
  ec44c6c1675c25b9827aacd08c02433cccde7780 third_party/googletest (release-1.8.0)
- 2761122b810fe8861004ae785cc3ab39f384d342 third_party/protobuf (v3.5.0)
+ b5fbb742af122b565925987e65c08957739976a7 third_party/protobuf (v3.5.2)
  cacf7f1d4e3d44d871b605da3b647f07d718623f third_party/zlib (v1.2.11)
  3be1924221e1326df520f8498d704a5c4c8d0cce third_party/cares/cares (cares-1_13_0)
  73594cde8c9a52a102c4341c244c833aa61b9c06 third_party/bloaty