fix the regression of building remote url (#935)

examples/remoteBuild.md

@@ -10,7 +10,7 @@ Running `kustomize build` against the url gives the same output.
 
 <!-- @remoteBuild @test -->
 ```
-target=github.com/kubernetes-sigs/kustomize//examples/multibases?ref=v1.0.6
+target=github.com/kubernetes-sigs/kustomize//examples/multibases
 test 3 == \
   $(kustomize build $target | grep cluster-a-.*-myapp-pod | wc -l); \
   echo $?

pkg/git/cloner.go

@@ -68,9 +68,8 @@ func ClonerUsingGitExec(repoSpec *RepoSpec) error {
 			"trouble adding remote %s",
 			repoSpec.CloneSpec())
 	}
-
 	if repoSpec.ref == "" {
-		return nil
+		repoSpec.ref = "master"
 	}
 	cmd = exec.Command(
 		gitProgram,