Replant tree (needed for example tests).

.travis.yml

@@ -5,7 +5,8 @@ go:
 
 go_import_path: sigs.k8s.io/kustomize
 
-sudo: false
+# Maybe, maybe not.
+# sudo: false
 
 # Only clone the most recent commit.
 git:
@@ -16,6 +17,7 @@ env:
 
 before_install:
   - source ./bin/consider-early-travis-exit.sh
+  - sudo apt-get install tree
   - curl -sfL https://install.goreleaser.com/github.com/golangci/golangci-lint.sh | sh -s -- -b $GOPATH/bin ${GOLANGCI_RELEASE}
   - go get -u github.com/monopole/mdrip