Decrease the precision of the sec_fraction in the tests

We were using picoseconds as precision but some Ruby implementations
only support up to nanoseconds. Since that much precision was not needed
to test the feature I decreased the precision.

activesupport/test/core_ext/time_ext_test.rb

@@ -110,17 +110,17 @@ def test_seconds_until_end_of_day_at_daylight_savings_time_end
   end
 
   def test_sec_fraction
-    time = Time.utc(2016, 4, 23, 0, 0, Rational(1, 10000000000))
-    assert_equal Rational(1, 10000000000), time.sec_fraction
+    time = Time.utc(2016, 4, 23, 0, 0, Rational(1, 1_000_000_000))
+    assert_equal Rational(1, 1_000_000_000), time.sec_fraction
 
-    time = Time.utc(2016, 4, 23, 0, 0, 0.0000000001)
-    assert_equal 0.0000000001.to_r, time.sec_fraction
+    time = Time.utc(2016, 4, 23, 0, 0, 0.000_000_001)
+    assert_equal Rational(1, 1_000_000_000), time.sec_fraction
 
-    time = Time.utc(2016, 4, 23, 0, 0, 0, Rational(1, 10000))
-    assert_equal Rational(1, 10000000000), time.sec_fraction
+    time = Time.utc(2016, 4, 23, 0, 0, 0, Rational(1, 1_000))
+    assert_equal Rational(1, 1_000_000_000), time.sec_fraction
 
-    time = Time.utc(2016, 4, 23, 0, 0, 0, 0.0001)
-    assert_equal 0.0001.to_r / 1000000, time.sec_fraction
+    time = Time.utc(2016, 4, 23, 0, 0, 0, 0.001)
+    assert_equal Rational(1, 1_000_000_000), time.sec_fraction
   end
 
   def test_beginning_of_day