title: Rails 5, scope opposite to another scope
body: <p>Is there any way in Rails 5 that I can use the opposite (negation) of a scope? 
  For example, given I have the following scope</p>
  
  <p><code>scope :missing_coordinates, -&gt; { where(latitude: [nil, '']).or(where(longitude: [nil, ''])) }</code></p>
  
  <p>is there any way I can use the opposite of that scope like: </p>
  
  <p><code>Places.not(missing_coordinates)</code> </p>
  
  <p>which would return the ones that have both the latitude and longitude?</p>