Update paper_trail gem to 4.2.0

Closes #426

Gemfile

@@ -20,12 +20,7 @@ gem 'figaro', '1.1.1'
 gem 'pg',                        '0.19.0'
 gem 'ransack',                   '1.5.1' # for searching
 gem 'validates_email_format_of', '1.6.3' # validates email against RFC 2822 and RFC 3696
-
-# with polymorphic fix
-gem 'paper_trail',
-  github: 'airblade/paper_trail',
-  ref: 'a453811226ec4ea59753ba6b827e390ced2fc140'
-# NB! if this gets upgraded, ensure Setting.reload_settings! still works correctly
+gem 'paper_trail', '~> 4.0'
 gem 'rails-settings-cached',     '0.4.1' # for settings
 
 # html-xml

Gemfile.lock

@@ -1,13 +1,3 @@
-GIT
-  remote: https://github.com/airblade/paper_trail.git
-  revision: a453811226ec4ea59753ba6b827e390ced2fc140
-  ref: a453811226ec4ea59753ba6b827e390ced2fc140
-  specs:
-    paper_trail (4.0.0.beta3)
-      activerecord (>= 3.0, < 6.0)
-      activesupport (>= 3.0, < 6.0)
-      request_store (~> 1.1.0)
-
 GIT
   remote: https://github.com/internetee/company_register.git
   revision: da7130542304fc543c90d54cd037d019a777c526
@@ -266,6 +256,10 @@ GEM
     nori (2.6.0)
     open4 (1.3.4)
     orm_adapter (0.5.0)
+    paper_trail (4.2.0)
+      activerecord (>= 3.0, < 6.0)
+      activesupport (>= 3.0, < 6.0)
+      request_store (~> 1.1)
     pdfkit (0.6.2)
     pg (0.19.0)
     polyamorous (1.3.1)
@@ -323,7 +317,8 @@ GEM
       i18n
       polyamorous (~> 1.1)
     rdoc (4.3.0)
-    request_store (1.1.0)
+    request_store (1.4.1)
+      rack (>= 1.4)
     responders (2.4.1)
       actionpack (>= 4.2.0, < 6.0)
       railties (>= 4.2.0, < 6.0)
@@ -476,7 +471,7 @@ DEPENDENCIES
   mina (= 0.3.1)
   money-rails
   nokogiri
-  paper_trail!
+  paper_trail (~> 4.0)
   pdfkit (= 0.6.2)
   pg (= 0.19.0)
   pry (= 0.10.1)