Bump rexml from 3.3.3 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.3 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@v3.3.3...v3.3.9)

---
updated-dependencies:
- dependency-name: rexml
  dependency-version: 3.3.9
  dependency-type: indirect
...

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

Author: dependabot[bot]

Gemfile.lock

@@ -37,8 +37,7 @@ GEM
     rake (13.0.6)
     rbzip2 (0.3.0)
     regexp_parser (2.7.0)
-    rexml (3.3.3)
-      strscan
+    rexml (3.3.9)
     rubocop (0.93.1)
       parallel (~> 1.10)
       parser (>= 2.7.1.5)
@@ -55,7 +54,6 @@ GEM
       sigdump (~> 0.2.2)
     sigdump (0.2.5)
     strptime (0.2.5)
-    strscan (3.1.0)
     test-unit (3.5.7)
       power_assert
     tzinfo (2.0.6)