Bump rexml from 3.2.6 to 3.2.8 (#1814)

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.6 to 3.2.8.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.2.6...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>

Gemfile.lock

@@ -381,7 +381,8 @@ GEM
       actionpack (>= 5.0)
       railties (>= 5.0)
     retryable (3.0.5)
-    rexml (3.2.6)
+    rexml (3.2.8)
+      strscan (>= 3.0.9)
     rinku (2.0.6)
     rolify (6.0.0)
     rspec (3.11.0)
@@ -482,6 +483,7 @@ GEM
     sshkit (1.21.2)
       net-scp (>= 1.1.2)
       net-ssh (>= 2.8.0)
+    strscan (3.1.0)
     sync (0.5.0)
     temple (0.9.1)
     term-ansicolor (1.7.1)