Bump msgpack from 1.5.4 to 1.5.5

Bumps [msgpack](https://github.com/msgpack/msgpack-ruby) from 1.5.4 to 1.5.5.
- [Release notes](https://github.com/msgpack/msgpack-ruby/releases)
- [Changelog](https://github.com/msgpack/msgpack-ruby/blob/master/ChangeLog)
- [Commits](msgpack/msgpack-ruby@v1.5.4...v1.5.5)

---
updated-dependencies:
- dependency-name: msgpack
  dependency-type: indirect
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Gemfile.lock

@@ -134,7 +134,7 @@ GEM
     mini_portile2 (2.8.0)
     minitest (5.16.3)
     mocha (1.14.0)
-    msgpack (1.5.4)
+    msgpack (1.5.5)
     net-imap (0.2.3)
       digest
       net-protocol