Fix linter errors.

[anshulpundir]

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 "lint" git@github.com:anshulpundir/swarmkit.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.

[codecov]

Codecov Report

Merging #2377 into master will increase coverage by 0.03%.
The diff coverage is 92.3%.

@@            Coverage Diff            @@
##           master   #2377      +/-   ##
=========================================
+ Coverage   60.37%   60.4%   +0.03%     
=========================================
  Files         128     128              
  Lines       26305   26267      -38     
=========================================
- Hits        15881   15866      -15     
+ Misses       9025    9008      -17     
+ Partials     1399    1393       -6

[dperny]

LGTM