Fixed a minor syntax error in test_nil

[InvisibleTech]

I have included the diff below. I used my version to complete the koans for about_data_types.rb as a test of my changes.

diff --git a/koans/about_data_types.rb b/koans/about_data_types.rb
index ad6cb89..cd7ea72 100644
--- a/koans/about_data_types.rb
+++ b/koans/about_data_types.rb
@@ -51,7 +51,7 @@ class AboutDataTypes < EdgeCase::Koan
end
def test_nil
@col.insert({:value => nil})

• assert_instance_of___, @col.find_one['value']
• assert_instance_of ___, @col.find_one['value']
  end
  def test_not_attribute
  @col.insert({:value => true})