chore(deps): bump rexml from 3.3.1 to 3.3.8

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.1 to 3.3.8.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.3.1...v3.3.8)

---
updated-dependencies:
- dependency-name: rexml
  dependency-type: indirect
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -168,8 +168,7 @@ GEM
       http-cookie (>= 1.0.2, < 2.0)
       mime-types (>= 1.16, < 4.0)
       netrc (~> 0.8)
-    rexml (3.3.1)
-      strscan
+    rexml (3.3.9)
     rollbar (3.5.2)
     rspec (3.13.0)
       rspec-core (~> 3.13.0)
@@ -239,7 +238,6 @@ GEM
       lint_roller (~> 1.1)
       rubocop-performance (~> 1.21.0)
     statsd-ruby (1.5.0)
-    strscan (3.1.0)
     tilt (2.4.0)
     timecop (0.9.10)
     tzinfo (2.0.6)