Cannot have duplicate keys in keyed each

[till]

Describe the bug

So first off, kudos for building svend3r. It bridges Svelte and D3 very nicely. :)

I have been trying a few of the examples and they do work, however, when I put my own data into it. It dies with an error of "Cannot have duplicate keys in keyed each".

To Reproduce

Steps to reproduce the behavior:

• take any example
• adjust the data to have a duplicate value for the "y"

Example of data that triggers it (copied from the bar chart):

export default [
  { letter: 'A', frequency: 0.08167 },
  { letter: 'B', frequency: 0.08167 }
];

Expected behavior

I was expecting to see two bars of equal height in the chart.