Bump rexml from 3.3.6 to 3.3.9 in /pgq-processors

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] <support@github.com>

pgq-processors/Gemfile.lock

@@ -80,8 +80,7 @@ GEM
       http-cookie (>= 1.0.2, < 2.0)
       mime-types (>= 1.16, < 4.0)
       netrc (~> 0.8)
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.9)
     rspec (3.10.0)
       rspec-core (~> 3.10.0)
       rspec-expectations (~> 3.10.0)
@@ -99,7 +98,6 @@ GEM
     sorted_set (1.0.3)
       rbtree
       set (~> 1.0)
-    strscan (3.1.0)
     syslog-logger (1.6.8)
     timeout (0.3.2)
     tzinfo (2.0.4)