Update Rubocop from 0.35.1 to 0.38.0.

Discussed in #14233.

See [their releases](https://github.com/bbatsov/rubocop/releases) for
more info.

Changes:
- Enable DisplayCopNames for lint output.
- Default behavior for `Alias` changed, set to enforce `prefer_alias_method`.
- Enabling Rails cops changed to new syntax.
- Remove StyleGuides and move Descriptions to comments.
- Add missing cops.
- Add TODOs for cops that should be enabled in the future.
- Set TargetRubyVersion to 2.1.

Gemfile

@@ -285,7 +285,7 @@ group :development, :test do
   gem 'spring-commands-spinach',  '~> 1.0.0'
   gem 'spring-commands-teaspoon', '~> 0.0.2'
 
-  gem 'rubocop', '~> 0.35.0', require: false
+  gem 'rubocop', '~> 0.38.0', require: false
   gem 'scss_lint', '~> 0.47.0', require: false
   gem 'coveralls',  '~> 0.8.2', require: false
   gem 'simplecov', '~> 0.10.0', require: false

Gemfile.lock

@@ -61,9 +61,7 @@ GEM
       faraday_middleware-multi_json (~> 0.0)
       oauth2 (~> 1.0)
     asciidoctor (1.5.3)
-    ast (2.1.0)
-    astrolabe (1.3.1)
-      parser (~> 2.2)
+    ast (2.2.0)
     attr_encrypted (1.3.4)
       encryptor (>= 1.3.0)
     attr_required (1.0.0)
@@ -554,8 +552,8 @@ GEM
     orm_adapter (0.5.0)
     paranoia (2.1.4)
       activerecord (~> 4.0)
-    parser (2.2.3.0)
-      ast (>= 1.1, < 3.0)
+    parser (2.3.0.6)
+      ast (~> 2.2)
     pg (0.18.4)
     poltergeist (1.9.0)
       capybara (~> 2.1)
@@ -615,7 +613,7 @@ GEM
       activesupport (= 4.2.5.2)
       rake (>= 0.8.7)
       thor (>= 0.18.1, < 2.0)
-    rainbow (2.0.0)
+    rainbow (2.1.0)
     raindrops (0.15.0)
     rake (10.5.0)
     raphael-rails (2.1.2)
@@ -687,13 +685,12 @@ GEM
     rspec-retry (0.4.5)
       rspec-core
     rspec-support (3.3.0)
-    rubocop (0.35.1)
-      astrolabe (~> 1.3)
-      parser (>= 2.2.3.0, < 3.0)
+    rubocop (0.38.0)
+      parser (>= 2.3.0.6, < 3.0)
       powerpack (~> 0.1)
       rainbow (>= 1.99.1, < 3.0)
       ruby-progressbar (~> 1.7)
-      tins (<= 1.6.0)
+      unicode-display_width (~> 1.0, >= 1.0.1)
     ruby-fogbugz (0.2.1)
       crack (~> 0.4)
     ruby-progressbar (1.7.5)
@@ -843,6 +840,7 @@ GEM
     unf (0.1.4)
       unf_ext
     unf_ext (0.0.7.1)
+    unicode-display_width (1.0.2)
     unicorn (4.9.0)
       kgio (~> 2.6)
       rack
@@ -1013,7 +1011,7 @@ DEPENDENCIES
   rqrcode-rails3 (~> 0.1.7)
   rspec-rails (~> 3.3.0)
   rspec-retry
-  rubocop (~> 0.35.0)
+  rubocop (~> 0.38.0)
   ruby-fogbugz (~> 0.2.1)
   sanitize (~> 2.0)
   sass-rails (~> 5.0.0)