Bump gon from 5.1.2 to 6.4.0

Bumps [gon](https://github.com/gazay/gon) from 5.1.2 to 6.4.0.
- [Release notes](https://github.com/gazay/gon/releases)
- [Changelog](https://github.com/gazay/gon/blob/master/CHANGELOG.md)
- [Commits](gazay/gon@v5.1.2...v6.4.0)

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

Author: dependabot[bot]

Gemfile

@@ -9,7 +9,7 @@ end
 gem 'rails', '~> 4.2.11.3'
 
 gem 'braintree'
-gem 'gon', '~> 5.1.2'
+gem 'gon', '~> 6.4.0'
 
 # respond_to methods have been extracted to the responders gem
 # http://edgeguides.rubyonrails.org/upgrading_ruby_on_rails.html#responders

Gemfile.lock

@@ -299,11 +299,11 @@ GEM
       activemodel (>= 4.2, < 5.2)
       activerecord (>= 4.2, < 5.2)
       request_store (~> 1.0)
-    gon (5.1.2)
-      actionpack (>= 2.3.0)
-      json
+    gon (6.4.0)
+      actionpack (>= 3.0.20)
+      i18n (>= 0.7)
       multi_json
-      request_store (>= 1.0.5)
+      request_store (>= 1.0)
     gravtastic (3.2.6)
     groupdate (4.1.2)
       activesupport (>= 4.2)
@@ -392,7 +392,9 @@ GEM
       mini_mime (>= 0.1.1)
     method_source (0.8.2)
     mime-types (2.99.3)
-    mimemagic (0.3.2)
+    mimemagic (0.4.3)
+      nokogiri (~> 1)
+      rake
     mina (0.3.8)
       open4 (~> 1.3.4)
       rake
@@ -414,7 +416,7 @@ GEM
       monetize (~> 1.4.0)
       money (~> 6.7)
       railties (>= 3.0)
-    multi_json (1.13.1)
+    multi_json (1.15.0)
     multi_xml (0.6.0)
     multipart-post (2.0.0)
     nested_form (0.3.2)
@@ -615,7 +617,8 @@ GEM
     refinerycms-settings (3.0.0)
       friendly_id (~> 5.0, >= 5.0.1)
       refinerycms-core (~> 3.0, >= 3.0.0)
-    request_store (1.1.0)
+    request_store (1.5.0)
+      rack (>= 1.4)
     responders (2.4.1)
       actionpack (>= 4.2.0, < 6.0)
       railties (>= 4.2.0, < 6.0)
@@ -825,7 +828,7 @@ DEPENDENCIES
   formtastic (~> 3.1.5)
   formtastic-bootstrap
   friendly_id (~> 5.1.0)
-  gon (~> 5.1.2)
+  gon (~> 6.4.0)
   gravtastic
   groupdate
   guard-rspec (~> 4.2.8)