use markdownlint docker image in drone

.drone.yml

@@ -17,13 +17,9 @@ steps:
   - curl -L https://github.com/thegeeklab/hugo-geekblog/releases/latest/download/hugo-geekblog.tar.gz | tar -xz -C themes/hugo-geekblog/ --strip-components=1
 
 - name: markdownlint
-  image: node:lts-alpine
+  image: thegeeklab/markdownlint-cli
   commands:
-  - npm install -g markdownlint-cli
   - markdownlint 'content/**/*.md' 'README.md'
-  environment:
-    FORCE_COLOR: true
-    NPM_CONFIG_LOGLEVEL: error
 
 - name: spellcheck
   image: node:lts-alpine
@@ -114,6 +110,6 @@ depends_on:
 
 ---
 kind: signature
-hmac: 9804d6d37d7aab27cc51ce360e8efdafb71aae2fb0592df720dbc6a4625b2a28
+hmac: 01fdb24010e4027cb131ca2138b50164ad62a574b565ed05642a22f95a89c368
 
 ...