title: Amberframework Granite decimal number in model
body: <p>I have a Rails application running Postgres with model containing decimal field.
  Now I'm creating an Amber API with Granite.
  How do I define a decimal field in my model in Crystal?</p>
  <pre><code>class User &lt; Granite::Base
    connection pg
    table users
  
    column id : Int64, primary: true
    column api_token : String
    column points : Float64 # this does not work
  end
  </code></pre>
  <p>I get a runtime error:</p>
  <blockquote>
  <p>PG::ResultSet#read returned a PG::Numeric. A Float64 was expected.</p>
  </blockquote>