Update the govuk_frontend_toolkit to 4.9.0

# 4.9.0

- Add websafe organisation colours
- Split colours into two files with backwards-compatible colours.scss
replacement

# 4.8.2

- Add GOV.UK lint to lint scss files (PR alphagov#260)
- Remove reference to old colour palette (PR alphagov#256)
- Fix link to GOV.UK elements - tabular data

# 4.8.1

- Update DEFRA brand colour to new green (PR alphagov#249)

# 4.8.0

- Pass cohort name to analytics when using multivariate test (PR alphagov#251)

# 4.7.0

- Add 'mailto' tracking to GOV.UK Analytics (PR alphagov#244)

package.json

@@ -7,7 +7,7 @@
     "node": ">=4.0.0"
   },
   "dependencies": {
-    "govuk_frontend_toolkit": "^4.6.1"
+    "govuk_frontend_toolkit": "^4.9.0"
   },
   "devDependencies": {
     "consolidate": "^0.10.0",