Bump rexml from 3.2.6 to 3.3.6

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.6 to 3.3.6.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.2.6...v3.3.6)

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

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

Gemfile.lock

@@ -369,7 +369,8 @@ GEM
       http-cookie (>= 1.0.2, < 2.0)
       mime-types (>= 1.16, < 4.0)
       netrc (~> 0.8)
-    rexml (3.2.6)
+    rexml (3.3.6)
+      strscan
     rspec (3.13.0)
       rspec-core (~> 3.13.0)
       rspec-expectations (~> 3.13.0)
@@ -446,6 +447,7 @@ GEM
     stringio (3.1.0)
     stripe (1.58.0)
       rest-client (>= 1.4, < 4.0)
+    strscan (3.1.0)
     table_print (1.5.7)
     test-unit (3.6.1)
       power_assert