Switch from direct dependency on money gem to monetize gem

This change is actually made around Spree 2.0, but we missed it. The `monetize` gem also installs the `money` gem.

Gemfile

@@ -27,7 +27,7 @@ gem 'cancan', '~> 1.6.10'
 gem 'ffaker'
 gem 'highline', '2.0.3' # Necessary for the install generator
 gem 'json'
-gem 'money', '< 6.1.0'
+gem 'monetize', '~> 1.1'
 gem 'paranoia', '~> 2.4'
 gem 'ransack', '~> 1.8.10'
 gem 'state_machines-activerecord'

Gemfile.lock

@@ -448,9 +448,10 @@ GEM
     mini_racer (0.2.15)
       libv8 (> 7.3)
     minitest (5.14.3)
-    money (5.0.0)
-      i18n (~> 0.4)
-      json
+    monetize (1.9.4)
+      money (~> 6.12)
+    money (6.13.8)
+      i18n (>= 0.6.4, <= 2)
     msgpack (1.3.3)
     multi_json (1.15.0)
     multi_xml (0.6.0)
@@ -781,7 +782,7 @@ DEPENDENCIES
   knapsack
   letter_opener (>= 1.4.1)
   mini_racer (= 0.2.15)
-  money (< 6.1.0)
+  monetize (~> 1.1)
   oauth2 (~> 1.4.4)
   ofn-qz!
   oj