Fix deprecation warnings on white_list_sanitizer

The recent update to v1.1.0 of rails_html_sanitizer means that rspec is
raising lots of deprecation warnings. This is a bug in that version and
and is resolved by updating to v1.2.0.

See issue here: rails/rails#36858

Gemfile.lock

@@ -300,7 +300,7 @@ GEM
     rails-dom-testing (2.0.3)
       activesupport (>= 4.2.0)
       nokogiri (>= 1.6)
-    rails-html-sanitizer (1.1.0)
+    rails-html-sanitizer (1.2.0)
       loofah (~> 2.2, >= 2.2.2)
     rails-i18n (5.1.3)
       i18n (>= 0.7, < 2)