Bump net-imap from 0.2.3 to 0.3.1

Bumps [net-imap](https://github.com/ruby/net-imap) from 0.2.3 to 0.3.1.
- [Release notes](https://github.com/ruby/net-imap/releases)
- [Commits](https://github.com/ruby/net-imap/compare/v0.2.3...v0.3.1)

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

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

Gemfile.lock

@@ -305,10 +305,8 @@ GEM
     naught (1.1.0)
     nenv (0.3.0)
     nested_form (0.3.2)
-    net-imap (0.2.3)
-      digest
+    net-imap (0.3.1)
       net-protocol
-      strscan
     net-pop (0.1.1)
       digest
       net-protocol
@@ -520,7 +518,6 @@ GEM
       actionpack (>= 5.2)
       activesupport (>= 5.2)
       sprockets (>= 3.0.0)
-    strscan (3.0.3)
     sysexits (1.2.0)
     temple (0.8.2)
     thor (1.2.1)