Update rubocop to current

Gemfile

@@ -229,7 +229,7 @@ group :development do
   gem 'haml_lint', '~> 0.24.0'
   gem 'spring-commands-rspec'
   # for static code analisys
-  gem 'rubocop', '~> 0.51.0', require: false
+  gem 'rubocop', require: false
   # as database
   gem 'sqlite3'
   # to open mails

Gemfile.lock

@@ -74,7 +74,7 @@ GEM
       airbrake-ruby (~> 2.5)
     airbrake-ruby (2.7.0)
     arel (7.1.4)
-    ast (2.3.0)
+    ast (2.4.0)
     autoprefixer-rails (7.1.1)
       execjs
     awesome_nested_set (3.1.3)
@@ -326,9 +326,9 @@ GEM
     paper_trail (9.0.0)
       activerecord (>= 4.2, < 5.3)
       request_store (~> 1.1)
-    parallel (1.12.0)
-    parser (2.4.0.2)
-      ast (~> 2.3)
+    parallel (1.12.1)
+    parser (2.5.1.0)
+      ast (~> 2.4.0)
     pdf-core (0.2.5)
     phantomjs (2.1.1.0)
     piwik_analytics (1.0.2)
@@ -469,11 +469,11 @@ GEM
       rspec-mocks (~> 3.6.0)
       rspec-support (~> 3.6.0)
     rspec-support (3.6.0)
-    rubocop (0.51.0)
+    rubocop (0.55.0)
       parallel (~> 1.10)
-      parser (>= 2.3.3.1, < 3.0)
+      parser (>= 2.5)
       powerpack (~> 0.1)
-      rainbow (>= 2.2.2, < 3.0)
+      rainbow (>= 2.2.2, < 4.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (~> 1.0, >= 1.0.1)
     ruby-oembed (0.12.0)
@@ -539,7 +539,7 @@ GEM
     unf (0.1.4)
       unf_ext
     unf_ext (0.0.7.2)
-    unicode-display_width (1.3.0)
+    unicode-display_width (1.3.2)
     unicode_utils (1.4.0)
     unobtrusive_flash (3.1.0)
       railties
@@ -661,7 +661,7 @@ DEPENDENCIES
   rqrcode
   rspec-activemodel-mocks
   rspec-rails (~> 3.5, >= 3.5.2)
-  rubocop (~> 0.51.0)
+  rubocop
   ruby-oembed (~> 0.12.0)
   sass-rails (>= 4.0.2)
   selectize-rails