Create an array of unique values, in order, from the input arrays
$ npm install --save array-union
```js const arrayUnion = require('array-union');
arrayUnion([1, 1, 2, 3], [2, 3]); //=> [1, 2, 3]
arrayUnion(['foo', 'foo', 'bar'], ['foo']); //=> ['foo', 'bar'] ```
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