[Where] fix unit test.

Author: reegeek

src/StructLinq.Tests/WhereTests.cs

@@ -9,7 +9,7 @@ public class WhereTests : AbstractEnumerableTests<int>
     {
         protected override IEnumerable<int> Build(int size)
         {
-            return StructEnumerable.Range(-1, size).Where(x => x >= -1);
+            return StructEnumerable.Range(-1, size).Where(x => x >= -1, x=>x);
         }
 
         [Fact]