formatted npm completion and used helper function

clean_files.txt

@@ -72,6 +72,7 @@ completion/available/knife.completion.bash
 completion/available/kontena.completion.bash
 completion/available/kubectl.completion.bash
 completion/available/minikube.completion.bash
+completion/available/npm.completion.bash
 completion/available/packer.completion.bash
 completion/available/pip.completion.bash
 completion/available/pip3.completion.bash

completion/available/npm.completion.bash

@@ -1,9 +1,7 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
+cite "about-completion"
+about-completion "npm (Node Package Manager) completion"
 
-# npm (Node Package Manager) completion
-# https://docs.npmjs.com/cli/completion
-
-if command -v npm &>/dev/null
-then
-  eval "$(npm completion)"
+if _command_exists npm; then
+	eval "$(npm completion)"
 fi