Bump rexml from 3.2.5 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.5 to 3.3.9.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.2.5...v3.3.9)

---
updated-dependencies:
- dependency-name: rexml
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Diff for: Gemfile

@@ -6,5 +6,5 @@ gem 'tzinfo-data', platforms: [:mswin, :mingw, :jruby]
 gem 'wdm', '~> 0.1', platforms: [:mswin, :mingw]
 gem 'middleman-blog', '~> 4.0'
 gem 'rack', '~> 2.2.3.1'
-gem 'rexml', '~> 3.2.7'
+gem 'rexml', '~> 3.3.9'
 gem 'webrick', '~> 1.8.2'

Diff for: Gemfile.lock

@@ -91,12 +91,10 @@ GEM
     rb-fsevent (0.11.0)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rexml (3.2.9)
-      strscan
+    rexml (3.3.9)
     sassc (2.4.0)
       ffi (~> 1.9)
     servolux (0.13.0)
-    strscan (3.1.2)
     temple (0.8.2)
     thor (1.1.0)
     tilt (2.0.10)
@@ -117,7 +115,7 @@ DEPENDENCIES
   middleman-autoprefixer (~> 2.7)
   middleman-blog (~> 4.0)
   rack (~> 2.2.3.1)
-  rexml (~> 3.2.7)
+  rexml (~> 3.3.9)
   tzinfo-data
   wdm (~> 0.1)
   webrick (~> 1.8.2)