we.easing[this.easing] is not a function error when using time based charts

[alcastaneda]

Expected behavior

When using time based charts, it seems to try to run an easein function that doesn't work, and it runs it often

Failure Logs

Code

 let values = [
      { label: "2018-10-23T15:27:56.688Z", values: { value: 2 } },
      { label: "2018-10-23T15:27:56.688Z", values: { value: 5 } },
      { label: "2018-10-25T15:27:56.688Z", values: { value: 3 } },
    ]
    // The liana.StatSerializer function serializes the result to a valid
    // JSONAPI payload.
    var json = new Liana.StatSerializer({ value: values }).perform();
    res.send(json);

Context

• Package Version: 2.15.2
• Express Version: 4.15.3
• Mongoose Version: 4.9.4
• MongoDB Version: 3.6.5