Add spring, a rails preloader alternative to zeus, to our gemfile

Add /bin to gitignore, bin is used by spring, rails preloader

.gitignore

@@ -43,3 +43,4 @@ vendor/bundle/
 coverage
 /reports/
 !/reports/README.md
+bin/

Gemfile

@@ -145,6 +145,8 @@ group :development do
   gem 'guard-rails'
   gem 'guard-rspec', '~> 4.7.3'
   gem 'rubocop', '>= 0.49.1'
+  gem 'spring', '=1.1.3'
+  gem 'spring-commands-rspec'
 
   # 1.0.9 fixed openssl issues on macOS https://github.com/eventmachine/eventmachine/issues/602
   # While we don't require this gem directly, no dependents forced the upgrade to a version

Gemfile.lock

@@ -696,6 +696,9 @@ GEM
       rails (>= 3.1)
     spreadsheet (1.1.4)
       ruby-ole (>= 1.0)
+    spring (1.1.3)
+    spring-commands-rspec (1.0.4)
+      spring (>= 0.9.1)
     sprockets (2.2.3)
       hike (~> 1.2)
       multi_json (~> 1.0)
@@ -839,6 +842,8 @@ DEPENDENCIES
   spree_auth_devise!
   spree_i18n!
   spree_paypal_express!
+  spring (= 1.1.3)
+  spring-commands-rspec
   stripe (~> 3.3.2)
   timecop
   truncate_html