Bump rubocop from 0.63.1 to 0.64.0

Bumps [rubocop](https://github.com/rubocop-hq/rubocop) from 0.63.1 to 0.64.0.
- [Release notes](https://github.com/rubocop-hq/rubocop/releases)
- [Changelog](https://github.com/rubocop-hq/rubocop/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop@v0.63.1...v0.64.0)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Gemfile.lock

@@ -94,7 +94,6 @@ GEM
     io-like (0.3.0)
     jaro_winkler (1.5.2)
     json (2.1.0)
-    kgio (2.11.2)
     loofah (2.2.3)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
@@ -148,7 +147,6 @@ GEM
       rake (>= 0.8.7)
       thor (>= 0.18.1, < 2.0)
     rainbow (3.0.0)
-    raindrops (0.19.0)
     rake (12.3.2)
     regexp_parser (1.3.0)
     rspec-core (3.8.0)
@@ -168,7 +166,7 @@ GEM
       rspec-mocks (~> 3.8.0)
       rspec-support (~> 3.8.0)
     rspec-support (3.8.0)
-    rubocop (0.63.1)
+    rubocop (0.64.0)
       jaro_winkler (~> 1.5.1)
       parallel (~> 1.10)
       parser (>= 2.5, != 2.5.1.1)
@@ -210,12 +208,6 @@ GEM
     uglifier (4.1.20)
       execjs (>= 0.3.0, < 3)
     unicode-display_width (1.4.1)
-    unicorn (5.4.0)
-      kgio (~> 2.6)
-      raindrops (~> 0.7)
-    unicorn-rails (2.2.1)
-      rack
-      unicorn
     xpath (3.2.0)
       nokogiri (~> 1.8)
 
@@ -247,7 +239,6 @@ DEPENDENCIES
   sprockets-rails (~> 3.2.1)
   sqlite3
   uglifier (>= 1.3.0)
-  unicorn-rails
 
 BUNDLED WITH
    1.16.2