Bump net-smtp from 0.1.0 to 0.3.1

Bumps [net-smtp](https://github.com/ruby/net-smtp) from 0.1.0 to 0.3.1.
- [Release notes](https://github.com/ruby/net-smtp/releases)
- [Changelog](https://github.com/ruby/net-smtp/blob/master/NEWS.md)
- [Commits](https://github.com/ruby/net-smtp/compare/v0.1.0...v0.3.1)

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

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

Gemfile.lock

@@ -323,7 +323,10 @@ GEM
       timeout
     net-protocol (0.1.3)
       timeout
-    net-smtp (0.1.0)
+    net-smtp (0.3.1)
+      digest
+      net-protocol
+      timeout
     nio4r (2.5.8)
     nokogiri (1.13.7)
       mini_portile2 (~> 2.8.0)