Typo in documentation of volume create

[usb79]

remove doubled negation (doesn't not => does not)

- What I did
fix a typo in the documentation of volume create (which is also used in the man page)

- How I did it
remove doubled negation (doesn't not => does not)

- How to verify it
have a look at the documentation before and after

- Description for the changelog
fix typo in documentation: remove doubled negation (doesn't not => does not)

- A picture of a cute animal (not mandatory but encouraged)
w c(..)o (
_(-) __)
/\ (
/()___)
w /|
|
m m

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "patch-1" git@github.com:usb79/cli.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[thaJeztah]

LGTM, thanks!