Bump rexml from 3.2.6 to 3.2.8

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>

Gemfile.lock

@@ -178,7 +178,8 @@ GEM
       parser (~> 3.2.0)
       rainbow (>= 2.0, < 4.0)
     regexp_parser (2.8.2)
-    rexml (3.2.6)
+    rexml (3.2.8)
+      strscan (>= 3.0.9)
     rspec (3.12.0)
       rspec-core (~> 3.12.0)
       rspec-expectations (~> 3.12.0)
@@ -229,6 +230,7 @@ GEM
       activesupport (>= 5.2)
       sprockets (>= 3.0.0)
     sqlite3 (1.4.2)
+    strscan (3.1.0)
     super_diff (0.10.0)
       attr_extras (>= 6.2.4)
       diff-lcs