[ref] migrate to rust edition 2018

.gitlab-ci.yml

lib/core/conf/Cargo.toml

lib/core/conf/keys.rs

lib/core/core/Cargo.toml

lib/core/core/cli/mod.rs

lib/core/core/cli/reset.rs

lib/core/core/lib.rs

lib/core/message/Cargo.toml

lib/core/message/events.rs

lib/core/message/lib.rs

lib/core/message/requests.rs

lib/core/module/Cargo.toml

lib/core/network/Cargo.toml

lib/core/network/events.rs

lib/core/network/lib.rs

lib/core/network/requests.rs

lib/modules/blockchain/blockchain-dal/Cargo.toml

lib/modules/blockchain/blockchain-dal/balance.rs

lib/modules/blockchain/blockchain-dal/block.rs

lib/modules/blockchain/blockchain-dal/certs.rs