build(deps): bump rexml in /packages/flutter/example/ios (#3285)

Bumps [rexml](https://github.com/ruby/rexml) from 3.4.1 to 3.4.2.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.4.1...v3.4.2)

---
updated-dependencies:
- dependency-name: rexml
  dependency-version: 3.4.2
  dependency-type: indirect
...

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

Author: dependabot[bot]

packages/flutter/example/ios/Gemfile.lock

@@ -179,7 +179,7 @@ GEM
       trailblazer-option (>= 0.1.1, < 0.2.0)
       uber (< 0.2.0)
     retriable (3.1.2)
-    rexml (3.4.1)
+    rexml (3.4.2)
     rouge (3.28.0)
     ruby2_keywords (0.0.5)
     rubyzip (2.4.1)