title: Rails: Validates greater_than_or_equal_to 0 does not work
body: <p>I shouldn't be able to set <code>user.fee_email = -1</code> but I can, even though I've specified in my model that the <code>numericality</code> of <code>fee_email</code> should be positive.</p>
  
  <p>Given:</p>
  
  <pre><code>class User &lt; ActiveRecord::Base
    validates :fee_email, numericality: { greater_than_or_equal_to: 0 }
  ...
  end
  </code></pre>
  
  <p>This should not happen:</p>
  
  <pre><code>2.2.1 :002 &gt; a = User.first
  2.2.1 :003 &gt; a.fee_email
   =&gt; #&lt;BigDecimal:43cbbe0,'0.0',9(27)&gt; 
  2.2.1 :004 &gt; a.fee_email = -1
   =&gt; -1 
  2.2.1 :005 &gt; a.fee_email
   =&gt; #&lt;BigDecimal:43b5688,'-0.1E1',9(27)&gt; 
  </code></pre>