Swap to_fs & to_formatted_s alias

Since rails/rails#44354 implements `to_formatted_s` as an alias for `to_fs`, it
makes sense for us to do it the same way.

lib/money/money.rb

@@ -222,7 +222,7 @@ def to_d
     value
   end
 
-  def to_formatted_s(style = nil)
+  def to_fs(style = nil)
     units = case style
     when :legacy_dollars
       2
@@ -241,8 +241,8 @@ def to_formatted_s(style = nil)
       sprintf("%s%d.%0#{units}d", sign, rounded_value.truncate, rounded_value.frac * (10 ** units))
     end
   end
-  alias_method :to_s, :to_formatted_s
-  alias_method :to_fs, :to_formatted_s
+  alias_method :to_s, :to_fs
+  alias_method :to_formatted_s, :to_fs
 
   def to_json(options = nil)
     if (options.is_a?(Hash) && options.delete(:legacy_format)) || Money.config.legacy_json_format

spec/money_spec.rb

@@ -71,14 +71,14 @@
     expect(non_fractional_money.to_s).to eq("1")
   end
 
-  it "to_formatted_s with a legacy_dollars style" do
-    expect(amount_money.to_formatted_s(:legacy_dollars)).to eq("1.23")
-    expect(non_fractional_money.to_formatted_s(:legacy_dollars)).to eq("1.00")
+  it "to_fs with a legacy_dollars style" do
+    expect(amount_money.to_fs(:legacy_dollars)).to eq("1.23")
+    expect(non_fractional_money.to_fs(:legacy_dollars)).to eq("1.00")
   end
 
-  it "to_formatted_s with a amount style" do
-    expect(amount_money.to_formatted_s(:amount)).to eq("1.23")
-    expect(non_fractional_money.to_formatted_s(:amount)).to eq("1")
+  it "to_fs with a amount style" do
+    expect(amount_money.to_fs(:amount)).to eq("1.23")
+    expect(non_fractional_money.to_fs(:amount)).to eq("1")
   end
 
   it "to_s correctly displays negative numbers" do
@@ -104,16 +104,16 @@
     expect(Money.new("999999999999999999.99", "USD").to_s).to eq("999999999999999999.99")
   end
 
-  it "to_formatted_s raises ArgumentError on unsupported style" do
-    expect{ money.to_formatted_s(:some_weird_style) }.to raise_error(ArgumentError)
+  it "to_fs raises ArgumentError on unsupported style" do
+    expect{ money.to_fs(:some_weird_style) }.to raise_error(ArgumentError)
   end
 
-  it "to_formatted_s is aliased as to_s for backward compatibility" do
-    expect(money.method(:to_s)).to eq(money.method(:to_formatted_s))
+  it "to_fs is aliased as to_s for backward compatibility" do
+    expect(money.method(:to_s)).to eq(money.method(:to_fs))
   end
 
-  it "to_formatted_s is aliased as to_fs for forward compatibility" do
-    expect(money.method(:to_fs)).to eq(money.method(:to_formatted_s))
+  it "to_fs is aliased as to_formatted_s for backward compatibility" do
+    expect(money.method(:to_formatted_s)).to eq(money.method(:to_fs))
   end
 
   it "legacy_json_format makes as_json return the legacy format" do