Remove deprecated assertion

Author: rafaelfranca

test/controllers/assigns_test.rb

@@ -19,8 +19,8 @@ def test_assigns
   def test_view_assigns
     @controller = ViewAssignsController.new
     process :test_assigns
-    assert_equal nil, assigns(:foo)
-    assert_equal nil, assigns[:foo]
+    assert_nil assigns(:foo)
+    assert_nil assigns[:foo]
     assert_equal "bar", assigns(:bar)
     assert_equal "bar", assigns[:bar]
   end