formatted kubectl completion and used helper function

clean_files.txt

@@ -70,6 +70,7 @@ completion/available/helm.completion.bash
 completion/available/jungle.completion.bash
 completion/available/knife.completion.bash
 completion/available/kontena.completion.bash
+completion/available/kubectl.completion.bash
 completion/available/packer.completion.bash
 completion/available/pip.completion.bash
 completion/available/pip3.completion.bash

completion/available/kubectl.completion.bash

@@ -1,8 +1,7 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
+cite "about-completion"
+about-completion "kubectl (Kubernetes CLI) completion"
 
-# kubectl (Kubernetes CLI) completion
-
-if command -v kubectl &>/dev/null
-then
+if _binary_exists kubectl; then
 	eval "$(kubectl completion bash)"
 fi