title: Issue with RANGE_ADD in Relay Mutations
body: <p>I was going through the relay docs and came to following code in RANGE_ADD.</p>
  
  <pre><code>class IntroduceShipMutation extends Relay.Mutation {
    // This mutation declares a dependency on the faction
    // into which this ship is to be introduced.
    static fragments = {
      faction: () =&gt; Relay.QL`fragment on Faction { id }`,
    };
    // Introducing a ship will add it to a faction's fleet, so we
    // specify the faction's ships connection as part of the fat query.
    getFatQuery() {
      return Relay.QL`
        fragment on IntroduceShipPayload {
          faction { ships },
          newShipEdge,
        }
      `;
    }
    getConfigs() {
      return [{
        type: 'RANGE_ADD',
        parentName: 'faction',
        parentID: this.props.faction.id,
        connectionName: 'ships',
        edgeName: 'newShipEdge',  
        rangeBehaviors: {
          // When the ships connection is not under the influence
          // of any call, append the ship to the end of the connection
          '': 'append',
          // Prepend the ship, wherever the connection is sorted by age
          'orderby(newest)': 'prepend',
        },
      }];
    }
    /* ... */
  }
  </code></pre>
  
  <p>Now over here it is mentioned that <code>edgeName</code> is required for adding new node to the connection. Looks well and fine.</p>
  
  <p>Now, I move further down the documentation and reached the <code>GraphQL</code> implementation of this mutation.</p>
  
  <pre><code>mutation AddBWingQuery($input: IntroduceShipInput!) {
    introduceShip(input: $input) {
      ship {
        id
        name
      }
      faction {
        name
      }
      clientMutationId
    }
  }
  </code></pre>
  
  <p>Now according to docs this mutation gives me output as </p>
  
  <pre><code>{
    "introduceShip": {
      "ship": {
        "id": "U2hpcDo5",
        "name": "B-Wing"
      },
      "faction": {
        "name": "Alliance to Restore the Republic"
      },
      "clientMutationId": "abcde"
    }
  }
  </code></pre>
  
  <p>I cannot see <code>edgeName</code> being present here.</p>
  
  <p>I was using graphene for my project. Over there also I saw something similar only </p>
  
  <pre><code>class IntroduceShip(relay.ClientIDMutation):
    class Input:
      ship_name = graphene.String(required=True)
      faction_id = graphene.String(required=True)
  
  ship = graphene.Field(Ship)
  faction = graphene.Field(Faction)
  
  @classmethod
  def mutate_and_get_payload(cls, input, context, info):
      ship_name = input.get('ship_name')
      faction_id = input.get('faction_id')
      ship = create_ship(ship_name, faction_id)
      faction = get_faction(faction_id)
      return IntroduceShip(ship=ship, faction=faction)
  </code></pre>
  
  <p>Over here also I cannot see <code>edgeName</code> anywhere. </p>
  
  <p>Any help please?  I am working on mutations for the first so wanted to confirm a m I missing something or is something wrong here? </p>