Update to Substrate rc4. (#214)

auction/Cargo.toml

auction/src/mock.rs

authority/Cargo.toml

authority/src/lib.rs

authority/src/mock.rs

benchmarking/Cargo.toml

benchmarking/src/lib.rs

benchmarking/src/tests.rs

currencies/Cargo.toml

currencies/src/mock.rs

currencies/src/tests.rs

gradually-update/Cargo.toml

gradually-update/src/mock.rs

gradually-update/src/tests.rs

oracle/Cargo.toml

oracle/rpc/Cargo.toml

oracle/rpc/runtime-api/Cargo.toml

oracle/src/lib.rs

oracle/src/mock.rs

oracle/src/tests.rs