Upgrade govuk_template to version 0.19.2

Fixes the following:

- Increase skiplink colour contrast
alphagov/govuk_template#263

- Fix Scala compile issues for Play template
alphagov/govuk_template#261

Gemfile.lock

@@ -123,7 +123,7 @@ GEM
     govuk_frontend_toolkit (5.0.2)
       rails (>= 3.1.0)
       sass (>= 3.2.0)
-    govuk_template (0.19.1)
+    govuk_template (0.19.2)
       rails (>= 3.1)
     hashery (2.1.1)
     hashie (3.4.4)
@@ -229,7 +229,7 @@ GEM
       rake (>= 0.8.7)
       thor (>= 0.18.1, < 2.0)
     rainbow (2.1.0)
-    rake (11.3.0)
+    rake (12.0.0)
     redis (3.2.1)
     rgeo (0.3.20)
     rgeo-geojson (0.3.1)