Bump net-imap from 0.3.8 to 0.3.9 in /ruby

Bumps [net-imap](https://github.com/ruby/net-imap) from 0.3.8 to 0.3.9.
- [Release notes](https://github.com/ruby/net-imap/releases)
- [Commits](ruby/net-imap@v0.3.8...v0.3.9)

---
updated-dependencies:
- dependency-name: net-imap
  dependency-version: 0.3.9
  dependency-type: indirect
...

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

Author: dependabot[bot]

ruby/Gemfile.lock

@@ -1419,7 +1419,7 @@ GEM
     multi_json (1.15.0)
     mustermann (3.0.3)
       ruby2_keywords (~> 0.0.1)
-    net-imap (0.3.8)
+    net-imap (0.3.9)
       date
       net-protocol
     net-pop (0.1.2)