Update rake Gem to v12

Specifically to pick up ruby/rake#211, which is required for Rails 6.1 support; without it, we get `undefined method \`with_application' for Rake:Module (NoMethodError)` when trying to run any rails script.

Note that we specifically implement this by updating the `scss_lint` gem to pick up the change "Relax gem dependency constraints to allow rake 12.x"

- https://github.com/sds/scss-lint/blob/master/CHANGELOG.md#0510
- https://github.com/ruby/rake/releases/tag/v12.2.0

Gemfile

@@ -243,7 +243,7 @@ group :development, :staging, :levelbuilder do
   gem 'rubocop-performance', require: false
   gem 'rubocop-rails', require: false
   gem 'rubocop-rails-accessibility', require: false
-  gem 'scss_lint', require: false
+  gem 'scss_lint', '~> 0.51.0', require: false
 end
 
 # Reduce volume of production logs

Gemfile.lock

@@ -697,7 +697,7 @@ GEM
       thor (>= 0.20.3, < 2.0)
     rainbow (3.0.0)
     raindrops (0.20.0)
-    rake (11.3.0)
+    rake (12.3.3)
     rambling-trie (2.2.1)
     rb-fsevent (0.11.2)
     rb-inotify (0.10.1)
@@ -783,8 +783,8 @@ GEM
     scenic-mysql_adapter (1.0.1)
       mysql2
       scenic (>= 1.4.0)
-    scss_lint (0.49.0)
-      rake (>= 0.9, < 12)
+    scss_lint (0.51.0)
+      rake (>= 0.9, < 13)
       sass (~> 3.4.20)
     selenium-webdriver (3.141.0)
       childprocess (~> 0.5)
@@ -1041,7 +1041,7 @@ DEPENDENCIES
   sassc-rails!
   scenic
   scenic-mysql_adapter
-  scss_lint
+  scss_lint (~> 0.51.0)
   selenium-webdriver (= 3.141.0)
   sequel
   shotgun