Update to govuk-elements-sass v3.1.1

[gemmaleigh]

3.1.1

• Only make column headers bold, not row headers (PR #483)
• De-duplicate legends/headings when there is one question per page by placing the heading for the question inside the legend of the fieldset (PR #507).
• Set cursor: default for for both the disabled input and the label - for radio buttons and checkboxes (PR #519).
• Fix stray line on checkboxes on IE11 caused by miscalculation of the border width of rotated element (PR #520).
• Fix hard error in details.polyfill.js raised when the <details> element doesn't follow the specified structure (PR #521).

3.1.0

• Split the list of partials imported by GOV.UK elements into two further files - elements and frontend-toolkit. This supports npm-sass, where the frontend toolkit dependencies are imported separately (PR #489).
• Add a new class .body-text for use inside legends, for text to accompany radio buttons or checkboxes - either 'select one', or 'select all that apply'. Ensure legends or elements within legends have margins in webkit browsers (PR #484).
• Move the breadcrumb so it sits outside the main element (PR #478)
• Constrain error summary boxes to 2/3 of the page width (PR #477)
• Remove the right padding from the last column of items in a table, also remove color set for table headers and cells, to allow users to change colour settings (PR #482
• Align table captions to the left (PR #476).
• Add guidance for use of table captions (PR #488).
• Fix unnecessary float and width 100% for .form-section and .form-group (PR #487).
• Fix incorrect margin above the last panel in a group (PR #498).
• Add guidance for the mininum text size to be used with the highlight box on confimation boxes (PR #481).

Changes made to the prototype kit

• Update markup for confirmation page, to ensure the text size is large enough. Fixes The text on the confirmation page needs to be bigger #390.
• Add a back link to the check your answers page. Fixes Check your answers template needs a back link #413.
• Update markup for date of birth pattern. Fixes Date example markup is out of step with Elements #412.
• Update link to blank question page from tips and tricks page. Fixes The link to Question page on Tips and tricks page is broken #376.
• De-duplicate legends/headings when there is one question per page by placing the heading for the question inside the legend of the fieldset
• Ensure form examples use normal weight form labels.
• Update details polyfill to ensure it isn't applied if the markup doesn't follow the GOV.UK elements example.

[hannalaakso]

Reviewed with @gemmaleigh and @alex-ju. Looks great :)