build(deps-dev): bump rexml in /cloud-sql/mysql/activerecord (#1461)

Author: dependabot[bot]

cloud-sql/mysql/activerecord/Gemfile.lock

@@ -163,7 +163,8 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rexml (3.2.6)
+    rexml (3.3.3)
+      strscan
     rspec-core (3.12.2)
       rspec-support (~> 3.12.0)
     rspec-expectations (3.12.3)
@@ -212,6 +213,7 @@ GEM
     sqlite3 (1.6.6)
       mini_portile2 (~> 2.8.0)
     sqlite3 (1.6.6-x86_64-linux)
+    strscan (3.1.0)
     thor (1.3.1)
     tilt (2.3.0)
     timeout (0.4.1)