bump friendly_id version to 5.0.3

Fixes #4350
Fix Spree::TaxonsHelper#taxon_preview not to show duplicate products

Fixes #4361
remove adjustments finalize!

According to commit 953c960680f284a2eb97b160a4610a72494ce107.
finalize event has been removed from Spree::Adjustment.
It will throw error in after_ship method since no finalize! method in adjustment now.
```
undefined method `finalize!' for #<Spree::Adjustment:0x000001095a1180>
```
move deliver email under completed_at touch, to avoid email to brake since the completead_at would be nil

Fixes #4363
Use can_supply in stead of deprecated in_stock in frontend

Fixes #4364
Bump factory_girl_rails to 4.4.0
Correct Rails version in readme
Bump Spree master to 2.2.1

Master should be higher then the latest stable branch.
Fixes incorrect order.item_total when line items have multiple currencies

Provides protection against order/line_item currency mismatch
Move currency update logic into it's own concern.
Bump the master branch to 2.3.0.beta
bump factory_girl to 4.4
Use OJ for faster JSON rendering
[api] Make products/index return unique products

It seems obvious in retrospect.
Show deleted shipping methods for shipping rates

Fixes #4328
Bump to 2.3.0.beta
Remove unused api/lib/spree/api/version.rb
Bump Paperclip to 4.1.1
Need to pass through a content-type when using upload_image to appease paperclip
Fixes #4304 - RABL cache collision for variants

This uses string prefixes within each variant template to ensure unique cache keys and guarantees no collisions.

Fixes #4308