Fix Money gem deprecation warning with :format

This removes millions of deprecation warnings like the following

```
[DEPRECATION] `symbol_position: :before` is deprecated - you can replace it with `format: %u %n`
```

from the build. It gets printed every time a `Spree::Money` is instantiated.

This should result in a non-negligible speed up of the test suite.

lib/spree/money.rb

@@ -10,15 +10,12 @@ module Spree
 
     def initialize(amount, options = {})
       @money = ::Monetize.parse([amount, (options[:currency] || Spree::Config[:currency])].join)
-      @options = {}
-      @options[:with_currency] = Spree::Config[:display_currency]
-      @options[:symbol_position] = Spree::Config[:currency_symbol_position].to_sym
-      @options[:no_cents] = Spree::Config[:hide_cents]
-      @options[:decimal_mark] = Spree::Config[:currency_decimal_mark]
-      @options[:thousands_separator] = Spree::Config[:currency_thousands_separator]
-      @options.merge!(options)
-      # Must be a symbol because the Money gem doesn't do the conversion
-      @options[:symbol_position] = @options[:symbol_position].to_sym
+
+      if options.key?(:symbol_position)
+        options[:format] = position_to_format(options.delete(:symbol_position))
+      end
+
+      @options = defaults.merge(options)
     end
 
     # Return the currency symbol (on its own) for the current default currency
@@ -47,5 +44,30 @@ module Spree
     def ==(other)
       @money == other.money
     end
+
+    private
+
+    def defaults
+      {
+        with_currency: Spree::Config[:display_currency],
+        no_cents: Spree::Config[:hide_cents],
+        decimal_mark: Spree::Config[:currency_decimal_mark],
+        thousands_separator: Spree::Config[:currency_thousands_separator],
+        format: position_to_format(Spree::Config[:currency_symbol_position])
+      }
+    end
+
+    def position_to_format(position)
+      return if position.nil?
+
+      case position.to_sym
+      when :before
+        '%u%n'
+      when :after
+        '%n %u'
+      else
+        raise 'Invalid symbol position'
+      end
+    end
   end
 end

spec/lib/spree/money_spec.rb

@@ -82,6 +82,11 @@ describe Spree::Money do
       money = Spree::Money.new(10, html: false)
       expect(money.to_s).to eq("10.00 $")
     end
+
+    it 'raises with invalid position' do
+      expect { Spree::Money.new(10, symbol_position: 'invalid') }
+        .to raise_error('Invalid symbol position')
+    end
   end
 
   context "EUR" do