Use SpawnNamed instead of Spawn in Overseer (#1430)

* Use SpawnNamed instead of Spawn in Overseer

* reexport SpawnNamed and fix doc tests

* Fix deps

polkadot/node/primitives/Cargo.toml

@@ -11,3 +11,4 @@ polkadot-statement-table = { path = "../../statement-table" }
 parity-scale-codec = { version = "1.3.0", default-features = false, features = ["derive"] }
 runtime_primitives = { package = "sp-runtime", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 async-trait = "0.1"
+sp-core = { git = "https://github.com/paritytech/substrate", branch = "master" }

polkadot/node/primitives/src/lib.rs

@@ -35,6 +35,8 @@ use polkadot_statement_table::{
 	v1::Misbehavior as TableMisbehavior,
 };
 
+pub use sp_core::traits::SpawnNamed;
+
 /// A statement, where the candidate receipt is included in the `Seconded` variant.
 ///
 /// This is the committed candidate receipt instead of the bare candidate receipt. As such,