eslint-plugin-flowtype does not validate
<p>I am trying to configure <code>eslint + babel-eslint + eslint-plugin-react + eslint-plugin-flowtype</code></p>

<p>I have the following <code>devDependencies</code> in <code>package.json</code>:</p>

<pre><code>"babel-eslint": "^7.1.1",
"eslint": "^3.10.2",
"eslint-config-airbnb": "^13.0.0",
"eslint-plugin-flowtype": "^2.25.0",
"eslint-plugin-import": "^2.2.0",
"eslint-plugin-jsx-a11y": "^2.2.3",
"eslint-plugin-react": "^6.7.1"
</code></pre>

<p>And the following <code>.eslinrc</code>:</p>

<pre><code>{
  "parser": "babel-eslint",
  "plugins": [
    "flowtype"
  ],
  "extends": [
    "airbnb",
    "plugin:flowtype/recommended"
  ],
  "rules": {
    "max-len": [1, 80, 2, {"ignoreComments": true}],
    "prop-types": [0],
    "react/jsx-filename-extension": [1, { "extensions": [".js", ".jsx"] }],
    "react/prefer-stateless-function": [
      0,
      {
        "ignorePureComponents": true
      }
    ],
    "no-console": 0
  },
  "settings": {
    "flowtype": {
      "onlyFilesWithFlowAnnotation": true
    }
  }
}
</code></pre>

<p>I wrote simple code example in <code>App.js</code>:</p>

<pre><code>function foo() {
  const a: string = 1;
  return a;
}

async function bar() {
  const b = await foo();
  return b;
}
</code></pre>

<p>If I launch <code>eslint src/App.js</code> then <code>eslint</code> does not show any messages.
If I add <code>"flowtype/require-return-type": 2</code> into <code>.eslintrc</code> then <code>eslint</code> shows:</p>

<pre><code>error  Missing return type annotation  flowtype/require-return-type
error  Missing return type annotation  flowtype/require-return-type
✖ 2 problems (2 errors, 0 warnings)
</code></pre>

<p>But I don't understand why <code>const a: string = 1;</code> is valid.
How to enable checking type of <code>const a: string = 1;</code>?</p>