Fix Failing Linter

[dthomson25]

I got the following errors when I run the linter on master:

reposerver/repository/repository_test.go:255:49: composites: `*github.com/argoproj/argo-cd/pkg/apis/application/v1alpha1.KustomizeImageTag` composite literal uses unkeyed fields (govet)
	assert.Equal(t, []*argoappv1.KustomizeImageTag{{"nginx", "1.15.4"}, {"k8s.gcr.io/nginx-slim", "0.8"}}, res.Kustomize.ImageTags)
	                                               ^
util/util.go:104:10: nilness: tautological condition: non-nil != nil (govet)
		if err != nil {
		       ^
make: *** [lint] Error 1```
The following PR address these issues.

[codecov-io]

Codecov Report

Merging #1350 into master will increase coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1350      +/-   ##
==========================================
+ Coverage    37.5%   37.51%   +<.01%     
==========================================
  Files          59       59              
  Lines        9113     9112       -1     
==========================================
  Hits         3418     3418              
+ Misses       5186     5185       -1     
  Partials      509      509

Impacted Files	Coverage Δ
util/util.go	12.32% <0%> (+0.16%)	⬆️

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