Bump rexml from 3.2.5 to 3.2.8 (#350)

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.5 to 3.2.8.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](https://github.com/ruby/rexml/compare/v3.2.5...v3.2.8)

---
updated-dependencies:
- dependency-name: rexml
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Riccardo Graziosi <31478034+riggraz@users.noreply.github.com>

Gemfile.lock

@@ -218,7 +218,8 @@ GEM
     responders (3.0.1)
       actionpack (>= 5.0)
       railties (>= 5.0)
-    rexml (3.2.5)
+    rexml (3.2.8)
+      strscan (>= 3.0.9)
     rspec-core (3.12.2)
       rspec-support (~> 3.12.0)
     rspec-expectations (3.12.3)
@@ -253,6 +254,7 @@ GEM
       activesupport (>= 5.2)
       sprockets (>= 3.0.0)
     stripe (11.2.0)
+    strscan (3.1.0)
     thor (1.3.1)
     tilt (2.0.10)
     timeout (0.4.1)