Bump net-smtp from 0.5.0 to 0.5.1

Bumps [net-smtp](https://github.com/ruby/net-smtp) from 0.5.0 to 0.5.1.
- [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/v0.5.0...v0.5.1)

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

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

Gemfile.lock

@@ -106,7 +106,7 @@ GEM
       ruby2_keywords (~> 0.0.1)
     net-protocol (0.2.2)
       timeout
-    net-smtp (0.5.0)
+    net-smtp (0.5.1)
       net-protocol
     netrc (0.11.0)
     nio4r (2.7.4)