Update govuk template mustache to the latest version

[gemmaleigh]

https://raw.githubusercontent.com/alphagov/govuk_template/master/CHANGEL OG.md

0.18.1

• Remove gov.uk prefix from relative links when printing ([PR

  234](https://github.com/alphagov/govuk_template/pull/234))

• Fix a .visually-hidden bug on GOV.UK ([PR

  177](https://github.com/alphagov/govuk_template/pull/177))

  0.18.0

• Publish the Jinja version of the template to NPM
• Update HTML5 Shiv to the latest version
• Remove an errant font loader script that was only being used for IE8

  0.17.3

• Fix colour of H2 headings in footer

  0.17.2

• Fix a bug with the skip-to-content link and iOS Voiceover
• Migrate @viewport statement from govuk_frontend_toolkit

  0.17.1

• Reduce file size of template: removes HTML comments, type attributes on scripts, and uses HTML5 charset declaration. #208
• Switch external link media query to be mobile first #205
• Sass file cleanups
  • Replace old grid mixins with newer grid from frontend toolkit #134
  • Remove duplicate grey variables #201

    0.17.0

• Add CSS hook (.js-hidden) for hiding content when JS is enabled. Some apps have an equivalent hook, which can be removed once upgraded to this version

  0.16.4

• Fix publish the Jinja version of the template with a package.json for those consuming it with NPM

  0.16.3

• make the Django version of the template into a proper Python package
• publish the Jinja version of the template with a package.json for those consuming it with NPM

  0.16.2

• more static assets added to assets.precompile to improve compatibility with apps running rails > 4.2.5

  0.16.1

• Fix colour of logo when in :active state