Update govuk_template from 0.5.1 to 0.6.2

https://github.com/alphagov/govuk_template/compare/v0.5.1...v0.6.2

Changes include:

- GOV.UK focus style on buttons
- Visited link colour changing
- OGL heading is text
- Touch and opengraph icons updated with new typeface
Merge pull request #289 from alphagov/update-govuk-template-0-6-2

Update govuk_template from 0.5.1 to 0.6.2