Fixed Test::Aggregate dependency.

It used to depend on Test::Aggregate::Nested which is not a separate
distribution.

Makefile.PL

@@ -27,7 +27,7 @@ test_requires 'FindBin'                 => 0;
 test_requires 'IO::All'                 => '0.41';
 test_requires 'Path::Class'             => '0.16';
 test_requires 'MooseX::NonMoose'        => '0.16';
-test_requires 'Test::Aggregate::Nested' => '0.363';
+test_requires 'Test::Aggregate'         => '0.363';
 
 author_requires 'Test::Pod'             => '1.22';
 author_requires 'Test::Pod::Coverage'   => '1.08';