Go back to the Spree's branch we use for step6

The fix introduced with https://github.com/coopdevs/spree/pull/2 was
already merged so we can point back to the `spree-upgrade-step-6`
branch.

Gemfile

@@ -10,7 +10,7 @@ gem 'i18n-js', '~> 3.0.0'
 gem 'nokogiri', '>= 1.6.7.1'
 
 gem 'pg'
-gem 'spree', github: 'coopdevs/spree', branch: 'fix-odd-even'
+gem 'spree', github: 'coopdevs/spree', branch: 'spree-upgrade-step-6'
 gem 'spree_i18n', github: 'spree/spree_i18n', branch: '1-3-stable'
 gem 'spree_auth_devise', github: 'openfoodfoundation/spree_auth_devise', branch: 'spree-upgrade-intermediate'
 

Gemfile.lock

@@ -8,8 +8,8 @@ GIT
 
 GIT
   remote: git://github.com/coopdevs/spree.git
-  revision: 3cd52439c3f78fb4fd6e5d72a4623bc8ff96d32b
-  branch: fix-odd-even
+  revision: 598cae8456260073cc0bcf85004b67fb02b8724c
+  branch: spree-upgrade-step-6
   specs:
     spree (1.3.99)
       spree_api (= 1.3.99)
@@ -778,4 +778,4 @@ RUBY VERSION
    ruby 2.1.5p273
 
 BUNDLED WITH
-   1.15.2
+   1.15.3