flatten-array: update to v1.1.0 of canonical tests

https://github.com/exercism/x-common/blob/d7a3c09b6758a8a5d59a2e140e6684031316280a/exercises/flatten-array/canonical-data.json

exercises/flatten-array/src/test/java/FlattenerTest.java

 import static java.util.Collections.singletonList;
 import static org.junit.Assert.assertEquals;
 
+/*
+ * version: 1.1.0
+ */
 public final class FlattenerTest {
 
     private Flattener flattener;
     }
 
     @Test
+    public void testFlatListIsPreserved() {
+        assertEquals(
+          asList(0, '1', "two"),
+            flattener.flatten(
+              asList(
+                0,
+                '1',
+                "two")));
+    }
+
+    @Ignore
+    @Test
     public void testASingleLevelOfNestingWithNoNulls() {
         assertEquals(
           asList(1, '2', 3, 4, 5, "six", "7", 8),