Require colon in timezone offset for Time.rfc3339

Fixes #77

Author: jeremyevans

lib/time.rb

@@ -660,7 +660,7 @@ def rfc3339(time)
           [T\s]
           (\d\d):(\d\d):(\d\d)
           (\.\d+)?
-          (Z|[+-]\d\d:?\d\d)
+          (Z|[+-]\d\d:\d\d)
           \s*\z/ix
       _xmlschema(pattern, time)
     end

test/test_time.rb

@@ -123,10 +123,11 @@ def subtest_xmlschema_alias(method)
     t = Time.utc(1996, 12, 20, 0, 39, 57)
     s = "1996-12-19T16:39:57-08:00"
     assert_equal(t, Time.__send__(method, s))
-    assert_equal(t, Time.__send__(method, s.sub(/:(?=00\z)/, '')))
     if method == :rfc3339
+      assert_raise(ArgumentError) { Time.rfc3339(s.sub(/:(?=00\z)/, '')) }
       assert_raise(ArgumentError) { Time.rfc3339(s.sub(/:00\z/, '')) }
     else
+      assert_equal(t, Time.__send__(method, s.sub(/:(?=00\z)/, '')))
       assert_equal(t, Time.__send__(method, s.sub(/:00\z/, '')))
     end
     # There is no way to generate time string with arbitrary timezone.