title: MongoDB returns error "Can't canonicalize query" for sort function
body: <pre><code>db.getCollection('posts').find({}, {sort: {post_id: 1}})
  </code></pre>
  
  <p>is returning</p>
  
  <pre><code>error: {
    "$err" : "Can't canonicalize query: BadValue Unsupported projection option: sort: { post_id: 1.0 }",
    "code" : 17287
  }
  </code></pre>
  
  <p>I'm baffled because I've run queries almost exactly like this in the past.  I'm running it through Robomongo but it does not work from my Meteor application either.  Can anybody explain what's going on?  </p>