Add `bundle` to release steps (#834)

Needed now that we added `Gemfile.lock`.

RELEASING

@@ -2,15 +2,16 @@ Releasing ShopifyAPI
 
 1. Check the Semantic Versioning page for info on how to version the new release: http://semver.org
 2. Update the version of ShopifyAPI in lib/shopify_api/version.rb
-3. Add a CHANGELOG entry for the new release
-4. Commit the changes with a commit message like "Packaging for release X.Y.Z"
-5. Tag the release with the version (Leave REV blank for HEAD or provide a SHA)
+3. Run `bundle`
+4. Add a CHANGELOG entry for the new release
+5. Commit the changes with a commit message like "Packaging for release X.Y.Z"
+6. Tag the release with the version (Leave REV blank for HEAD or provide a SHA)
   $ git tag vX.Y.Z REV
-6. Push out the changes
+7. Push out the changes
   $ git push
-7. Push out the tags
+8. Push out the tags
   $ git push --tags
-8. Publish the gem using Shipit
-9. Consider if the dependency in Shopify/shopify needs updated. It's used only by the tests so is a low risk change.
+9. Publish the gem using Shipit
+10. Consider if the dependency in Shopify/shopify needs updated. It's used only by the tests so is a low risk change.
 Also consider Shopify/shopify_app whose gemspec depends on this.
 We don't need to do this for every release, but we should try to keep them relatively up to date.