Bump rexml from 3.2.8 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.8 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@v3.2.8...v3.3.9)

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

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

Author: dependabot[bot]

Gemfile.lock

@@ -77,8 +77,7 @@ GEM
     regexp_parser (2.9.2)
     reline (0.5.7)
       io-console (~> 0.5)
-    rexml (3.2.8)
-      strscan (>= 3.0.9)
+    rexml (3.3.9)
     rouge (3.30.0)
     rubocop (1.42.0)
       json (~> 2.3)
@@ -102,7 +101,6 @@ GEM
     sassc (2.4.0)
       ffi (~> 1.9)
     stringio (3.1.0)
-    strscan (3.1.0)
     terminal-table (2.0.0)
       unicode-display_width (~> 1.1, >= 1.1.1)
     test-unit (3.6.2)