Bump rexml from 3.3.6 to 3.3.7

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.6 to 3.3.7.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.3.6...v3.3.7)

---
updated-dependencies:
- dependency-name: rexml
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Gemfile.lock

@@ -453,8 +453,7 @@ GEM
     responders (3.1.1)
       actionpack (>= 5.2)
       railties (>= 5.2)
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.7)
     rspec-core (3.13.0)
       rspec-support (~> 3.13.0)
     rspec-expectations (3.13.0)
@@ -569,7 +568,6 @@ GEM
       lint_roller (~> 1.1)
       rubocop-performance (~> 1.21.0)
     stringio (3.1.1)
-    strscan (3.1.0)
     terrapin (0.6.0)
       climate_control (>= 0.0.3, < 1.0)
     thor (1.3.2)