Bump net-imap from 0.4.9 to 0.4.9.1

Bumps [net-imap](https://github.com/ruby/net-imap) from 0.4.9 to 0.4.9.1.
- [Release notes](https://github.com/ruby/net-imap/releases)
- [Commits](ruby/net-imap@v0.4.9...v0.4.9.1)

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

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

Gemfile.lock

@@ -155,7 +155,7 @@ GEM
       ruby2_keywords (>= 0.0.5)
     msgpack (1.7.2)
     mutex_m (0.2.0)
-    net-imap (0.4.9)
+    net-imap (0.4.9.1)
       date
       net-protocol
     net-pop (0.1.2)