Temporarily revert #1619 until deploying successfully

Revert "Bump rexml from 3.3.2 to 3.3.3"
This reverts commit d3a49ca.

Author: yasulab

Gemfile.lock

@@ -371,7 +371,7 @@ GEM
     retriable (3.1.2)
     reverse_markdown (2.1.1)
       nokogiri
-    rexml (3.3.3)
+    rexml (3.3.2)
       strscan
     rspec-core (3.12.2)
       rspec-support (~> 3.12.0)