Bump plek from 3.0.0 to 4.0.0

Bumps [plek](https://github.com/alphagov/plek) from 3.0.0 to 4.0.0.
- [Release notes](https://github.com/alphagov/plek/releases)
- [Changelog](https://github.com/alphagov/plek/blob/master/CHANGELOG.md)
- [Commits](alphagov/plek@v3.0.0...v4.0.0)

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

Author: dependabot-preview[bot]

Gemfile

@@ -9,7 +9,7 @@ gem "govuk_ab_testing", "~> 2.4"
 gem "govuk_app_config", "~> 2.2"
 gem "govuk_publishing_components", "~> 21.56.1"
 gem "htmlentities", "~> 4.3"
-gem "plek", "~> 3.0"
+gem "plek", "~> 4.0"
 gem "rack_strip_client_ip", "~> 0.0.2"
 gem "rails", "~> 5.2.4"
 gem "rails-controller-testing", "~> 1.0"

Gemfile.lock

@@ -183,7 +183,7 @@ GEM
     parser (2.7.1.3)
       ast (~> 2.4.0)
     phantomjs (2.1.1.0)
-    plek (3.0.0)
+    plek (4.0.0)
     pry (0.13.1)
       coderay (~> 1.1)
       method_source (~> 1.0)
@@ -369,7 +369,7 @@ DEPENDENCIES
   jasmine-rails
   minitest-reporters
   mocha
-  plek (~> 3.0)
+  plek (~> 4.0)
   pry
   rack_strip_client_ip (~> 0.0.2)
   rails (~> 5.2.4)