Bump rexml from 3.3.6 to 3.3.9 (#146)

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.6 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@v3.3.6...v3.3.9)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -180,8 +180,7 @@ GEM
     redcarpet (3.6.0)
     request_store (1.5.1)
       rack (>= 1.4)
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.9)
     sass (3.7.4)
       sass-listen (~> 4.0.0)
     sass-listen (4.0.0)
@@ -203,7 +202,6 @@ GEM
       activesupport (>= 5.2)
       sprockets (>= 3.0.0)
     sqlite3 (1.4.4)
-    strscan (3.1.0)
     thor (1.2.1)
     thread_safe (0.3.6)
     tilt (2.0.11)