Bump rexml from 3.3.3 to 3.3.9 in /app/android

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-type: indirect
...

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

app/android/Gemfile.lock

@@ -171,8 +171,7 @@ GEM
       trailblazer-option (>= 0.1.1, < 0.2.0)
       uber (< 0.2.0)
     retriable (3.1.2)
-    rexml (3.3.3)
-      strscan
+    rexml (3.3.9)
     rouge (2.0.7)
     ruby2_keywords (0.0.5)
     rubyzip (2.3.2)
@@ -187,7 +186,6 @@ GEM
     simctl (1.6.10)
       CFPropertyList
       naturally
-    strscan (3.1.0)
     terminal-notifier (2.0.0)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)