title: lint-staged not running on precommit
body: <p>prettier is not running on precommit. This worked with the same configuration in other projects, so I'm baffled why it's not working this time. </p>
  
  <p>This is the relevant section of my package.json file:</p>
  
  <pre><code>"scripts": {
      "precommit": "lint-staged"
    },
  "lint-staged": {
    "*.{js,json,css,scss,html,md}": [
      "prettier --write",
      "git add"
    ]
  },
  </code></pre>
  
  <p>Edit. Here are the relevant devDependencies:</p>
  
  <pre><code>"devDependencies": {
    "husky": "^0.14.3",
    "lint-staged": "^7.0.4",
    "prettier": "1.12.0"
  },
  </code></pre>