Fix wording in order confirmation email template

Fixes issue #3063 "Repeated translation in Order Confirmation Screen and Email".
Now "Ready for" (collection time) is not repeated in place of "Collection
details" (collection instructions)

app/views/spree/order_mailer/_shipping.html.haml

@@ -50,6 +50,6 @@
   - if @order.order_cycle.andand.pickup_instructions_for(@order.distributor).present?
     %p
       %strong
-        = t :email_shipping_collection_time
+        = t :email_shipping_collection_instructions
       %br
       #{@order.order_cycle.pickup_instructions_for(@order.distributor)}