title: Merge ActionController::Parameters with rails 5
body: <p>In rails 4, I can merge! StrongParams, but since rails 5 (beta1) merge! is not available. Which is the best way to do that in a controller</p>
  
  <pre><code>  params = ActionController::Parameters.new({
               name: 'Francesco',
               age:  22,
               role: 'admin'
           })
           params.merge!(city: "Los Angeles")
  </code></pre>