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

@@ -257,7 +257,8 @@ GEM
       http-cookie (>= 1.0.2, < 2.0)
       mime-types (>= 1.16, < 4.0)
       netrc (~> 0.8)
-    rexml (3.2.6)
+    rexml (3.2.8)
+      strscan (>= 3.0.9)
     rollbar (2.27.1)
     rouge (4.1.3)
     rspec-core (3.12.2)
@@ -333,6 +334,7 @@ GEM
       rest-client (>= 1.8.0, < 3)
       storyblok-richtext-renderer (>= 0.0.4, < 1)
     storyblok-richtext-renderer (0.0.10)
+    strscan (3.1.0)
     thor (1.2.2)
     timecop (0.9.6)
     timeout (0.4.0)