Update haml_lint to work with newest rubocop

Gemfile

@@ -304,7 +304,7 @@ group :development, :test do
   gem 'rubocop', '~> 0.47.1', require: false
   gem 'rubocop-rspec', '~> 1.12.0', require: false
   gem 'scss_lint', '~> 0.47.0', require: false
-  gem 'haml_lint', '~> 0.18.2', require: false
+  gem 'haml_lint', '~> 0.21.0', require: false
   gem 'simplecov', '0.12.0', require: false
   gem 'flay', '~> 2.6.1', require: false
   gem 'bundler-audit', '~> 0.5.0', require: false

Gemfile.lock

@@ -319,10 +319,10 @@ GEM
       multi_json (>= 1.3.2)
     haml (4.0.7)
       tilt
-    haml_lint (0.18.2)
+    haml_lint (0.21.0)
       haml (~> 4.0)
-      rake (>= 10, < 12)
-      rubocop (>= 0.36.0)
+      rake (>= 10, < 13)
+      rubocop (>= 0.47.0)
       sysexits (~> 1.1)
     hamlit (2.6.1)
       temple (~> 0.7.6)
@@ -759,7 +759,7 @@ GEM
       rack (>= 1, < 3)
     thor (0.19.4)
     thread_safe (0.3.5)
-    tilt (2.0.5)
+    tilt (2.0.6)
     timecop (0.8.1)
     timfel-krb5-auth (0.8.3)
     tool (0.2.3)
@@ -888,7 +888,7 @@ DEPENDENCIES
   google-api-client (~> 0.8.6)
   grape (~> 0.18.0)
   grape-entity (~> 0.6.0)
-  haml_lint (~> 0.18.2)
+  haml_lint (~> 0.21.0)
   hamlit (~> 2.6.1)
   health_check (~> 2.2.0)
   hipchat (~> 1.5.0)