Fixing shell aliases module name mismatch

[RalfNorthman]

The Nushell book says:

Some users may prefer to think of this feature as multiple "shells within shells", where each has its own directory.

The Standard Library provides a set of aliases that can be used in place of the dirs commands above.

Import them using:

use std/dirs shell-aliases *

The built-in aliases are: ...

But the Nushell source code says

crates/nu-std/std/dirs/mod.nu

export module shells-aliases {
export alias shells = main
export alias enter = add
export alias dexit = drop

This PR aims to fix this mismatch.

[NotTheDr01ds]

Oops - That was my typo. Thanks for catching that!