Bump rexml from 3.4.0 to 3.4.2 in /asf-site-src

Bumps [rexml](https://github.com/ruby/rexml) from 3.4.0 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@v3.4.0...v3.4.2)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

asf-site-src/Gemfile.lock

@@ -108,7 +108,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.11.1)
       ffi (~> 1.0)
-    rexml (3.4.0)
+    rexml (3.4.2)
     rouge (3.30.0)
     sassc (2.4.0)
       ffi (~> 1.9)