Update base64 requirement from 0.11.0 to 0.12.3 (#1749)

* Update base64 requirement from 0.11.0 to 0.12.3

Updates the requirements on [base64](https://github.com/marshallpierce/rust-base64) to permit the latest version.
- [Release notes](https://github.com/marshallpierce/rust-base64/releases)
- [Changelog](https://github.com/marshallpierce/rust-base64/blob/master/RELEASE-NOTES.md)
- [Commits](https://github.com/marshallpierce/rust-base64/compare/v0.11.0...v0.12.3)

Signed-off-by: dependabot[bot] <support@github.com>

* protocols/gossipsub/CHANGELOG: Make dependency entry generic

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Max Inden <mail@max-inden.de>

protocols/gossipsub/CHANGELOG.md

@@ -1,7 +1,6 @@
 # 0.22.1 [unreleased]
 
-- Update lru-time-cache dependency.
-  [PR 1746](https://github.com/libp2p/rust-libp2p/pull/1746).
+- Update dependencies.
 
 # 0.22.0 [2020-09-09]
 

protocols/gossipsub/Cargo.toml

@@ -22,7 +22,7 @@ wasm-timer = "0.2.4"
 unsigned-varint = { version = "0.4.0", features = ["futures-codec"] }
 log = "0.4.8"
 sha2 = "0.8.1"
-base64 = "0.11.0"
+base64 = "0.12.3"
 smallvec = "1.1.0"
 prost = "0.6.1"
 hex_fmt = "0.3.0"