Upgrade paperclip dependency to fix security issue.

"It's possible to cause a DoS by uploading files with a spoofed media
type, because it causes megabytes of logging to be written."

See thoughtbot/paperclip#2017 and
thoughtbot/paperclip#2126

core/spree_core.gemspec

@@ -31,7 +31,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'highline', '~> 1.6.18' # Necessary for the install generator
   s.add_dependency 'kaminari', '~> 0.15', '>= 0.15.1'
   s.add_dependency 'monetize', '~> 1.1'
-  s.add_dependency 'paperclip', '~> 4.2.0'
+  s.add_dependency 'paperclip', '~> 4.3.0'
   s.add_dependency 'paranoia', '~> 2.1.0'
   s.add_dependency 'premailer-rails'
   s.add_dependency 'rails', '~> 4.2.6'