Bump msgpack from 1.7.2 to 1.7.3

Bumps [msgpack](https://github.com/msgpack/msgpack-ruby) from 1.7.2 to 1.7.3.
- [Changelog](https://github.com/msgpack/msgpack-ruby/blob/master/ChangeLog)
- [Commits](msgpack/msgpack-ruby@v1.7.2...v1.7.3)

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

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

Gemfile.lock

@@ -173,7 +173,7 @@ GEM
     minitest (5.25.1)
     mocha (2.4.5)
       ruby2_keywords (>= 0.0.5)
-    msgpack (1.7.2)
+    msgpack (1.7.3)
     net-http (0.4.1)
       uri
     net-imap (0.4.16)