Pin protobuf version to 2.8.x
Lighthouse doesn't build with protobuf 2.9.0, and there's no point
upgrading when it's about to be deleted.
@@ -8,7 +8,7 @@ description = "Google protobuf message and service definitions used in Lighthous
[dependencies]
futures = "0.1"
grpcio = { version = "0.4", default-features = false, features = ["protobuf-codec"] }
-protobuf = "2.0"
+protobuf = "~2.8.1"
[build-dependencies]
protoc-grpcio = "0.3.1"
