Update template and toolkit to latest versions

- Fix logo issues and document using tabindex to fix skiplink (template 0.18.3)
- Degrade gracefully when external JS can’t be loaded (template 0.18.2)
- Fix a .visually-hidden bug on GOV.UK (template 0.18.1)
- Slims down the page weight for IE8 (template 0.18.0)
- Amend GOVUK.stickAtTopWhenScrolling to "unstick" for smaller screens (toolkit 4.18.3)
- Remove `@media` width query from print CSS and use npm script rather than grunt-shell (toolkit 4.18.2)
- Fix error in IE from shimLinksWithButtonRole JS (toolkit 4.18.1)
- Add GOVUK.ShowHideContent JavaScript (toolkit 4.18.0)
- Add class to selection buttons per radio and checkbox (toolkit 4.17.0)
- Fix anchor-buttons.js (toolkit 4.16.1)
- Add Department for International Trade organisation (toolkit 4.16.0)
- Normalise keyboard behaviour between buttons and links with a button role (toolkit 4.15.0)
- Fixes a bug with the sizing of tabular numbers (toolkit 4.14.1)
- Makes headings block-level by default (toolkit 4.13.0)

Gemfile

@@ -40,11 +40,11 @@ group :development, :test do
 end
 
 gem 'plek', '1.11.0'
-gem 'govuk_frontend_toolkit', '~> 4.12.0'
+gem 'govuk_frontend_toolkit', '~> 4.18.3'
 
 if ENV['GOVUK_TEMPLATE_DEV']
   gem 'govuk_template', :path => "../govuk_template"
 else
-  gem 'govuk_template', '0.17.3'
+  gem 'govuk_template', '0.18.3'
 end
 gem 'gds-api-adapters', '26.7.0'

Gemfile.lock

@@ -85,10 +85,10 @@ GEM
     govuk-lint (0.6.1)
       rubocop (~> 0.35.0)
       scss_lint (~> 0.44.0)
-    govuk_frontend_toolkit (4.12.0)
+    govuk_frontend_toolkit (4.18.3)
       rails (>= 3.1.0)
       sass (>= 3.2.0)
-    govuk_template (0.17.3)
+    govuk_template (0.18.3)
       rails (>= 3.1)
     http-cookie (1.0.2)
       domain_name (~> 0.5)
@@ -256,8 +256,8 @@ DEPENDENCIES
   gds-api-adapters (= 26.7.0)
   govuk-content-schema-test-helpers (~> 1.4)
   govuk-lint (~> 0.6.0)
-  govuk_frontend_toolkit (~> 4.12.0)
-  govuk_template (= 0.17.3)
+  govuk_frontend_toolkit (~> 4.18.3)
+  govuk_template (= 0.18.3)
   image_optim (= 0.17.1)
   jasmine-rails (~> 0.10.6)
   logstasher (= 0.4.8)