Last of Array 
by Anthony Fu @antfu
> TypeScript 4.0 is recommended in this challenge
Implement a generic `Last` that takes an Array `T` and returns it's last element's type.
For example
```ts
type arr1 = ['a', 'b', 'c']
type arr2 = [3, 2, 1]
type tail1 = Last // expected to be 'c'
type tail2 = Last // expected to be 1
```
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