Use keys of different length in let & map alignment example

https://guide.clojure.style/#bindings-alignment
https://guide.clojure.style/#map-keys-alignment

:thing1 & :thing2 have the same length.
Use keys of different length in let & map alignment example, to make obvious that it's the keys to be aligned, not values.

```clojure
{:thing1 thing1
 :long-thing long-thing}
```
