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

@@ -210,7 +210,8 @@ GEM
     regexp_parser (2.9.0)
     reline (0.4.3)
       io-console (~> 0.5)
-    rexml (3.2.6)
+    rexml (3.2.8)
+      strscan (>= 3.0.9)
     rspec (3.13.0)
       rspec-core (~> 3.13.0)
       rspec-expectations (~> 3.13.0)
@@ -240,6 +241,7 @@ GEM
     ruby-progressbar (1.13.0)
     ruby2_keywords (0.0.5)
     stringio (3.1.0)
+    strscan (3.1.0)
     thor (1.3.1)
     timeout (0.4.1)
     tzinfo (2.0.6)