Bump loofah from 2.2.3 to 2.4.0 (#521)

Bumps [loofah](https://github.com/flavorjones/loofah) from 2.2.3 to 2.4.0.
- [Release notes](https://github.com/flavorjones/loofah/releases)
- [Changelog](https://github.com/flavorjones/loofah/blob/master/CHANGELOG.md)
- [Commits](https://github.com/flavorjones/loofah/compare/v2.2.3...v2.4.0)

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -97,7 +97,7 @@ GEM
     connection_pool (2.2.1)
     crack (0.4.3)
       safe_yaml (~> 1.0.0)
-    crass (1.0.4)
+    crass (1.0.5)
     database_cleaner (1.6.2)
     diff-lcs (1.3)
     docile (1.3.0)
@@ -166,7 +166,7 @@ GEM
       activesupport (>= 4)
       railties (>= 4)
       request_store (~> 1.0)
-    loofah (2.2.3)
+    loofah (2.4.0)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
     lumberjack (1.0.13)
@@ -193,7 +193,7 @@ GEM
     net-ssh-gateway (2.0.0)
       net-ssh (>= 4.0.0)
     netrc (0.11.0)
-    nokogiri (1.10.4)
+    nokogiri (1.10.7)
       mini_portile2 (~> 2.4.0)
     nokogumbo (1.5.0)
       nokogiri