Bump rexml from 3.3.3 to 3.3.9 (#232)

Author: dependabot[bot]

Gemfile.lock

@@ -104,8 +104,7 @@ GEM
     rb-inotify (0.10.1)
       ffi (~> 1.0)
     regexp_parser (2.1.1)
-    rexml (3.3.3)
-      strscan
+    rexml (3.3.9)
     rqrcode (2.2.0)
       chunky_png (~> 1.0)
       rqrcode_core (~> 1.0)
@@ -150,7 +149,6 @@ GEM
       simplecov_json_formatter (~> 0.1)
     simplecov-html (0.12.3)
     simplecov_json_formatter (0.1.4)
-    strscan (3.1.0)
     thor (1.3.0)
     ttfunk (1.7.0)
     tzinfo (2.0.6)