correct spelling mistake

[EdwardBetts]

No description provided.

[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 "spelling" git@github.com:EdwardBetts/docker-credential-helpers.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.

[eyJhb]

This can be closed - #124 .

[vdemeester]

Thanks @eyJhb @EdwardBetts