Fix ruby 2.4.0 deprecation warnings

spec/money_spec.rb

@@ -191,7 +191,7 @@ def expectation.fractional
     it "stores fractional as an integer regardless of what is passed into the constructor" do
       m = Money.new(100)
       expect(m.fractional).to eq 100
-      expect(m.fractional).to be_a(Fixnum)
+      expect(m.fractional).to be_a(Integer)
     end
 
     context "loading a serialized Money via YAML" do
@@ -351,7 +351,7 @@ def expectation.fractional
 
     it "returns a Fixnum when infinite_precision is not set" do
       money = Money.new(100, "USD")
-      expect(money.round_to_nearest_cash_value).to be_a Fixnum
+      expect(money.round_to_nearest_cash_value).to be_a Integer
     end
 
     it "returns a BigDecimal when infinite_precision is set", :infinite_precision do