Bump net-imap from 0.3.7 to 0.4.0

Bumps [net-imap](https://github.com/ruby/net-imap) from 0.3.7 to 0.4.0.
- [Release notes](https://github.com/ruby/net-imap/releases)
- [Commits](ruby/net-imap@v0.3.7...v0.4.0)

---
updated-dependencies:
- dependency-name: net-imap
  dependency-type: indirect
  update-type: version-update:semver-minor
...

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

Gemfile.lock

@@ -283,7 +283,7 @@ GEM
     msgpack (1.7.2)
     multi_json (1.15.0)
     mysql2 (0.5.5)
-    net-imap (0.3.7)
+    net-imap (0.4.0)
       date
       net-protocol
     net-pop (0.1.2)