Revert "Temporary ignored the failing specs for Date"

This reverts commit 17e64cca6b737060884f6fd9ab1c5055e9b49577.

The specs should work now.

library/date/iso8601_spec.rb

@@ -17,22 +17,18 @@
     d.should == Date.civil(-4712, 1, 1)
   end
 
-  ruby_version_is ""..."3.1" do
-    it "parses a Symbol into a Date object" do
-      d = Date.iso8601(:'2015-10-15')
-      d.should == Date.civil(2015, 10, 15)
-    end
+  it "parses a Symbol into a Date object" do
+    d = Date.iso8601(:'2015-10-15')
+    d.should == Date.civil(2015, 10, 15)
   end
 
   it "parses a StringSubclass into a Date object" do
     d = Date.iso8601(Class.new(String).new("-4712-01-01"))
     d.should == Date.civil(-4712, 1, 1)
   end
 
-  ruby_version_is ""..."3.1" do
-    it "raises an ArgumentError when passed a Symbol without a valid Date" do
-      -> { Date.iso8601(:test) }.should raise_error(ArgumentError)
-    end
+  it "raises an ArgumentError when passed a Symbol without a valid Date" do
+    -> { Date.iso8601(:test) }.should raise_error(ArgumentError)
   end
 
   it "raises a TypeError when passed an Object" do