Allow greater tolerance in RationalTest (#2898)

It has been reported that original tolerance was perhaps too strict, possibly preventing valid solutions from passing the test. Adjusting the tolerance to allow other valid solutions. The new tolerance value was copied from the Python implementation.  

Fixes #2823.

[no important files changed]

exercises/practice/rational-numbers/src/test/java/RationalTest.java

@@ -8,10 +8,10 @@ public class RationalTest {
 
     // Helper methods
 
-    private static final double DOUBLE_EQUALITY_TOLERANCE = 1e-15;
+    private static final double DOUBLE_EQUALITY_TOLERANCE = 1e-8;
 
     private void assertDoublesEqual(double x, double y) {
-        assertThat(x).isEqualTo(y, within(DOUBLE_EQUALITY_TOLERANCE));
+        assertThat(x).isCloseTo(y, within(DOUBLE_EQUALITY_TOLERANCE));
     }
 
     // Tests