Bump rexml from 3.2.4 to 3.2.5 in /docs_src

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.4 to 3.2.5.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.2.4...v3.2.5)

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

Author: dependabot[bot]

docs_src/Gemfile.lock

@@ -51,7 +51,7 @@ GEM
     rb-fsevent (0.10.4)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rexml (3.2.4)
+    rexml (3.2.5)
     rouge (3.22.0)
     safe_yaml (1.0.5)
     sassc (2.4.0)