libp2p-plaintext 0.21.0

Plaintext encryption dummy protocol for libp2p
Documentation
# 0.21.0 [2020-08-18]

- Bump `libp2p-core` dependency.

# 0.20.0 [2020-07-01]

- Updated dependencies.

# 0.19.1 [2020-06-22]

- Updated dependencies.