Merge pull request #1640 from coderdojo-japan/dependabot/bundler/rexml-3.3.9

Bump rexml from 3.3.6 to 3.3.9

Author: yasulab

Gemfile.lock

@@ -382,7 +382,7 @@ GEM
     retriable (3.1.2)
     reverse_markdown (2.1.1)
       nokogiri
-    rexml (3.3.7)
+    rexml (3.3.9)
     rspec-core (3.13.1)
       rspec-support (~> 3.13.0)
     rspec-expectations (3.13.3)