Bump rexml from 3.3.1 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.1 to 3.3.9.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.3.1...v3.3.9)

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

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

Gemfile.lock

@@ -355,8 +355,7 @@ GEM
     responders (3.1.1)
       actionpack (>= 5.2)
       railties (>= 5.2)
-    rexml (3.3.1)
-      strscan
+    rexml (3.3.9)
     rrrretry (1.0.0)
     rubocop (1.56.4)
       base64 (~> 0.1.1)
@@ -449,7 +448,6 @@ GEM
       rubocop-performance (~> 1.19.1)
     standardrb (1.0.1)
       standard
-    strscan (3.1.0)
     temple (0.8.2)
     test-prof (1.0.10)
     thor (1.3.1)