Bump govuk_frontend_toolkit to 5.1.1

# 5.1.1

- Update the alpha, beta and discovery colours to $govuk-blue to match
the updated phase banner ([PR
#370](alphagov/govuk_frontend_toolkit#370))
- Fix radio button show/hide behaviour when used outside a form ([PR
#375](alphagov/govuk_frontend_toolkit#375))
- Fix a "Stick at top when scrolling" component bug related to scroll
anchoring in Chrome 56+ ([PR
#376](alphagov/govuk_frontend_toolkit#376))
- Minor travis fixes ([PR
#373](alphagov/govuk_frontend_toolkit#373))

# 5.1.0

- Allow custom options when tracking events ([PR
#365](alphagov/govuk_frontend_toolkit#365))

# 5.0.3

- Change HMRC and DEFRA text colours for improved contrast ([PR
#368](alphagov/govuk_frontend_toolkit#368))

package.json

@@ -8,7 +8,7 @@
     "node": ">=6.0"
   },
   "dependencies": {
-    "govuk_frontend_toolkit": "^5.0.2"
+    "govuk_frontend_toolkit": "^5.1.1"
   },
   "devDependencies": {
     "body-parser": "^1.14.1",