Update rexml to version 3.3.6

Author: depfu[bot]

Gemfile.lock

@@ -47,7 +47,8 @@ GEM
     rake (13.0.6)
     randexp (0.1.7)
     regexp_parser (2.8.2)
-    rexml (3.2.6)
+    rexml (3.3.6)
+      strscan
     rspec (3.12.0)
       rspec-core (~> 3.12.0)
       rspec-expectations (~> 3.12.0)
@@ -154,6 +155,7 @@ GEM
       standard-custom (>= 1.0.1, < 2)
       standard-performance (>= 1.2, < 2)
       version_gem (>= 1.1.3, < 4)
+    strscan (3.1.0)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)
     unf (0.1.4)