upgrade dependencies

* rails, puma, bunny, mysql2
* remove createsend which isn't needed/used
* don't require highline all the time

Gemfile

@@ -1,7 +1,7 @@
 source 'https://rubygems.org'
-gem 'rails', '= 5.2.2.1'
-gem 'mysql2', '>= 0.3.18', '< 0.5'
-gem 'puma', '~> 3.0'
+gem 'rails', '= 5.2.4.1'
+gem 'mysql2'
+gem 'puma'
 gem 'turbolinks', '~> 5'
 gem 'haml'
 gem 'nifty-utils'
@@ -15,7 +15,7 @@ gem 'dynamic_form'
 gem 'changey'
 gem 'mail', :git => 'https://github.com/mikel/mail.git', :branch => '2-7-stable'
 gem 'autoprefixer-rails'
-gem 'bunny', '~> 2.5.1'
+gem 'bunny'
 gem 'secure_headers'
 gem 'chronic'
 gem 'basic_ssl'
@@ -27,9 +27,8 @@ gem 'sentry-raven'
 gem 'gelf'
 gem 'moonrope'
 gem 'jwt'
-gem 'createsend', '~> 4.0'
 gem 'acme-client'
-gem 'highline', :require => true
+gem 'highline', :require => false
 
 group :development, :assets do
   gem 'sass-rails', '~> 5.0'