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](https://github.com/ruby/rexml/compare/v3.2.6...v3.2.8)

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

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

Gemfile.lock

@@ -481,7 +481,8 @@ GEM
       io-console (~> 0.5)
     request_store (1.7.0)
       rack (>= 1.4)
-    rexml (3.2.6)
+    rexml (3.2.8)
+      strscan (>= 3.0.9)
     rinku (2.0.6)
     rotp (6.3.0)
     rouge (4.2.1)
@@ -560,6 +561,7 @@ GEM
     stringio (3.1.0)
     strong_migrations (1.8.0)
       activerecord (>= 5.2)
+    strscan (3.1.0)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)
     terser (1.2.2)