Bump rexml from 3.2.5 to 3.3.6 in /src/supermarket

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.5 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@v3.2.5...v3.3.6)

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

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

src/supermarket/Gemfile.lock

@@ -619,7 +619,8 @@ GEM
       http-cookie (>= 1.0.2, < 2.0)
       mime-types (>= 1.16, < 4.0)
       netrc (~> 0.8)
-    rexml (3.2.5)
+    rexml (3.3.6)
+      strscan
     rinku (2.0.6)
     rollout (2.5.0)
       redis (~> 4.0)
@@ -721,6 +722,7 @@ GEM
       unicode-display_width (>= 1.5, < 3.0)
       unicode_utils (~> 1.4)
     strings-ansi (0.2.0)
+    strscan (3.1.0)
     syslog-logger (1.6.8)
     terrapin (0.6.0)
       climate_control (>= 0.0.3, < 1.0)