Fixed SonarQube warnings

src/test/java/com/github/underscore/ChainingTest.java

@@ -164,8 +164,7 @@ void chainObj() {
                         .sortBy(item -> (Integer) item.get("age"))
                         .map(item -> item.get("name") + " is " + item.get("age"))
                         .first()
-                        .item()
-                        .toString();
+                        .item();
         assertEquals("moe is 21", youngest);
         new Underscore<>(stooges).of();
     }

src/test/java/com/github/underscore/UnderscoreTest.java

@@ -178,7 +178,7 @@ void push() {
     @Test
     void pop() {
         assertEquals("c", Underscore.pop(asList("a", "b", "c")).getKey());
-        assertEquals("c", new Underscore<>(asList("a", "b", "c")).pop().getKey().toString());
+        assertEquals("c", new Underscore<>(asList("a", "b", "c")).pop().getKey());
         assertEquals("c", Underscore.chain(asList("a", "b", "c")).pop().item().getKey());
     }
 
@@ -190,7 +190,7 @@ void pop() {
     @Test
     void shift() {
         assertEquals("a", Underscore.shift(asList("a", "b", "c")).getKey());
-        assertEquals("a", new Underscore<>(asList("a", "b", "c")).shift().getKey().toString());
+        assertEquals("a", new Underscore<>(asList("a", "b", "c")).shift().getKey());
         assertEquals("a", Underscore.chain(asList("a", "b", "c")).shift().item().getKey());
     }