无法使用变量通过 ansible 放置安装包

我有 ansible 脚本来安装我需要的应用程序。这是它的样子playbook：

- hosts: all
  become: true
  vars_files:
    - vars.yml
  strategy: free

  tasks:
   - name: Update and upgrade apt packages
     become: true
     apt:
       upgrade: yes
       update_cache: yes
       cache_valid_time: 86400 #One day
   - name: hack to resolve Problem with MergeList Issue
     shell: 'find /var/lib/apt/lists -maxdepth 1 -type f -exec rm -v {} \;'
   - name: update apt cache directly (apt module not reliable)
     shell: 'apt-get clean && apt-get update'
   - name: Preliminary installation
     apt:  name=apt-transport-https force=yes
   - name: Add the Google signing key
     apt_key: url=https://packages.cloud.google.com/apt/doc/apt-key.gpg  state=present
   - name: Add the k8s APT repo
     apt_repository: repo='deb http://apt.kubernetes.io/ kubernetes-xenial main' state=present
   - name: update apt cache directly (apt module not reliable)
     shell: 'apt-get update'
   - name: Install packages
     apt: name={{ item }} state=present force=yes
     with_items: "{{ PACKAGES }}"

安装我需要的软件包时，问题出现在最后一个任务中。错误：

TASK [Install packages] *******************************************************************************************************************************
failed: [192.168.77.11] (item=[u'vim  - htop  - tmux  - docker.io', u'kubelet', u'kubeadm', u'kubectl', u'kubernetes-cni']) => {"ansible_loop_var": "item", "changed": false, "item": ["vim  - htop  - tmux  - docker.io", "kubelet", "kubeadm", "kubectl", "kubernetes-cni"], "msg": "No package matching 'vim  - htop  - tmux  - docker.io' is available"}
failed: [192.168.77.10] (item=[u'vim  - htop  - tmux  - docker.io', u'kubelet', u'kubeadm', u'kubectl', u'kubernetes-cni']) => {"ansible_loop_var": "item", "changed": false, "item": ["vim  - htop  - tmux  - docker.io", "kubelet", "kubeadm", "kubectl", "kubernetes-cni"], "msg": "No package matching 'vim  - htop  - tmux  - docker.io' is available"}
failed: [192.168.77.12] (item=[u'vim  - htop  - tmux  - docker.io', u'kubelet', u'kubeadm', u'kubectl', u'kubernetes-cni']) => {"ansible_loop_var": "it---

文件内容vars.yml：

---
PACKAGES:
  - vim  - htop  - tmux  - docker.io
  - kubelet
  - kubeadm
  - kubectl
  - kubernetes-cni

我试图ssh通过apt-get. 一切都已成功安装并正常工作。版本ansible：2.8.5。服务器Ubuntu 16.04。告诉我可能出了什么问题？