Bump rexml from 3.2.5 to 3.3.3 (#29)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Diff for: Gemfile.lock

@@ -56,11 +56,13 @@ GEM
     rb-fsevent (0.10.3)
     rb-inotify (0.10.0)
       ffi (~> 1.0)
-    rexml (3.2.5)
+    rexml (3.3.3)
+      strscan
     rouge (3.13.0)
     safe_yaml (1.0.5)
     sassc (2.2.1)
       ffi (~> 1.9)
+    strscan (3.1.0)
     terminal-table (1.8.0)
       unicode-display_width (~> 1.1, >= 1.1.1)
     thread_safe (0.3.6)