title: Unable to turn off eslint no-unused-expressions
body: <p>I have created an app with create-react-app and I have applied the airbnb rules. The app also contains redux and flow.</p>
  
  <p>The following code is throwing the no-unused-expressions error in eslint:</p>
  
  <pre><code>const reducer = (state: string = '', action: Action) =&gt; {
      switch (action.type) {
          // cases
          default:
              (action: empty); // this is throwing eslint/no-unused-expressions
              return state;
      }
  };
  </code></pre>
  
  <p>I am trying to switch off the rule in eslintrc in order to replace it with flowtype/no-unused-expressions</p>
  
  <p>content of my .eslintrc.yml</p>
  
  <pre><code>extends:
      - airbnb
  parser: babel-eslint
  env:
      browser: true
      jest: true
  globals:
      SyntheticEvent: true,
  rules:
      no-unused-expressions: off
      react/prefer-stateless-function: off
      react/jsx-filename-extension: off
      react/jsx-one-expression-per-line: off
  </code></pre>
  
  <p>With this settings, the no-unused-expressions error is not shown anymore in the editor (vscode). However as soon as I compile with <code>npm run start</code> the error is still there:</p>
  
  <pre><code>Expected an assignment or function call and instead saw an expression  no-unused-expressions
  </code></pre>
  
  <p>causing it to fail to compile.</p>
  
  <p>Of course if I disable locally eslint for that rule for example with</p>
  
  <pre><code>// eslint-disable-line no-unused-expressions
  </code></pre>
  
  <p>Everything is working in both the editor and the browser. However, as I said I am trying to replace the eslint rule with the flowtype one exactly to avoid to be obliged to disable eslint every time I am using a flow type assertion.</p>
  
  <p>Any idea what I am doing wrong?</p>
  
  <p>package.json content:</p>
  
  <pre><code>{
    "name": "would-you-rather",
    "version": "0.1.0",
    "private": true,
    "dependencies": {
      "eslint-config-airbnb": "17.1.0",
      "eslint-config-flowtype-essential": "^1.0.0",
      "eslint-plugin-flowtype": "^3.2.0",
      "flow-bin": "0.89.0",
      "flow-typed": "2.5.1",
      "immutable": "4.0.0-rc.12",
      "prop-types": "15.6.2",
      "react": "16.6.3",
      "react-dom": "16.6.3",
      "react-icons": "3.2.2",
      "react-redux": "6.0.0",
      "react-redux-loading-bar": "4.1.0",
      "react-router-dom": "4.3.1",
      "react-scripts": "2.1.1",
      "redux": "4.0.1",
      "redux-immutable": "4.0.0",
      "redux-thunk": "2.3.0", 
      "semantic-ui-css": "2.4.1",
      "semantic-ui-react": "0.84.0"
    },
    "devDependencies": {
      "docdash": "1.0.1",
      "jsdoc": "3.5.5"
    },
    "scripts": {
      "start": "react-scripts start",
      "build": "react-scripts build",
      "test": "react-scripts test",
      "eject": "react-scripts eject",
      "jsdoc": "jsdoc --configure jsdoc.conf.json --recurse --private",
      "flow": "$(npm bin)/flow",
      "flow-typed": "$(npm bin)/flow-typed",
      "postinstall": "$(npm bin)/flow-typed install"
    },
    "browserslist": [
      "&gt;0.2%",
      "not dead",
      "not ie &lt;= 11",
      "not op_mini all"
    ]
  }
  </code></pre>
  
  <p><a href="https://github.com/luca-borrione/reactnd-project2-wouldyourather/tree/submitted" rel="nofollow noreferrer">Link of the project on github</a> if you want to play with it</p>