Update rexml (#3581)

Author: mattcreaser

build-support/Gemfile.lock

@@ -172,7 +172,7 @@ GEM
       trailblazer-option (>= 0.1.1, < 0.2.0)
       uber (< 0.2.0)
     retriable (3.1.2)
-    rexml (3.2.5)
+    rexml (3.2.8)
     rouge (2.0.7)
     ruby2_keywords (0.0.5)
     rubyzip (2.3.2)