build(deps): Bump multi_xml from 0.6.0 to 0.7.1

Bumps [multi_xml](https://github.com/sferik/multi_xml) from 0.6.0 to 0.7.1.
- [Changelog](https://github.com/sferik/multi_xml/blob/master/CHANGELOG.md)
- [Commits](sferik/multi_xml@v0.6.0...v0.7.1)

---
updated-dependencies:
- dependency-name: multi_xml
  dependency-type: indirect
  update-type: version-update:semver-minor
...

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

Gemfile.lock

@@ -209,7 +209,8 @@ GEM
     mocha (2.2.0)
       ruby2_keywords (>= 0.0.5)
     msgpack (1.7.2)
-    multi_xml (0.6.0)
+    multi_xml (0.7.1)
+      bigdecimal (~> 3.1)
     multipart-post (2.4.0)
     mutex_m (0.2.0)
     net-imap (0.4.10)