```ruby
app = lambda do |env|
    return [200, { "Content-Type" => "text/html" }, "hello <b>world</b>"]
end
run app
```

Update the Rack stub for Ruby 1.9 and Rack 1.0 compliance.
user
```ruby
app = lambda do |env|
    [200, { "Content-Type" => "text/html" }, ["hello <b>world</b>"]]
end
run app
```
assistant