Bump plek from 2.1.1 to 3.0.0

Bumps [plek](https://github.com/alphagov/plek) from 2.1.1 to 3.0.0.
- [Release notes](https://github.com/alphagov/plek/releases)
- [Changelog](https://github.com/alphagov/plek/blob/master/CHANGELOG.md)
- [Commits](alphagov/plek@v2.1.1...v3.0.0)

Gemfile

@@ -18,7 +18,7 @@ gem 'govuk_ab_testing', '~> 2.4'
 gem 'govuk_app_config', '~> 1.16'
 gem 'govuk_frontend_toolkit', '~> 8.2.0'
 gem 'govuk_publishing_components', '~> 16.26.0'
-gem 'plek', '~> 2.1'
+gem 'plek', '~> 3.0'
 gem 'slimmer', '~> 13.1'
 
 group :development, :test do

Gemfile.lock

@@ -191,7 +191,7 @@ GEM
     parser (2.6.3.0)
       ast (~> 2.4.0)
     phantomjs (2.1.1.0)
-    plek (2.1.1)
+    plek (3.0.0)
     pry (0.12.2)
       coderay (~> 1.1.0)
       method_source (~> 0.9.0)
@@ -368,7 +368,7 @@ DEPENDENCIES
   jasmine-rails
   minitest-reporters
   mocha
-  plek (~> 2.1)
+  plek (~> 3.0)
   pry-byebug
   puma
   rack_strip_client_ip (~> 0.0.2)