Revert govuk template to 0.12.0
Revert govuk template to 0.12.0

The GOV.UK text was missing from the header (next to the crown). Revert
to 0.12.0 for now until a fix is found.

TFOH/govuk_elements,TFOH/govuk_elements,gavboulton/govuk_elements,alphagov/govuk_elements,alphagov/govuk_elements,gavboulton/govuk_elements,gavboulton/govuk_elements,joelanman/govuk_elements,alphagov/govuk_elements,alphagov/govuk_elements,gavboulton/govuk_elements,joelanman/govuk_elements