title: Unexpected behaviour of rootDir and outDir
body: <p>I am trying to use TypeScript with React Native.</p>
  
  <p>This is my <code>tsconfig.json</code>:</p>
  
  <pre><code>{
      "compilerOptions": {
          "target": "es2015",
          "module": "es2015",
          "jsx": "react",
          "outDir": "build",
          "rootDir": "src",
          "allowSyntheticDefaultImports": true,
          "noImplicitAny": true,
          "experimentalDecorators": true,
          "preserveConstEnums": true,
          "allowJs": true,
          "sourceMap": true
      },
      "filesGlob": [
          "typings/index.d.ts",
          "src/**/*.ts",
          "src/**/*.tsx"
      ],
      "exclude": [
          "index.android.js",
          "index.ios.js",
          "build",
          "node_modules"
      ],
      "compileOnSave": false
  }
  </code></pre>
  
  <p>I would like all .ts(x) files in the src directory to be compiled to the build directory.</p>
  
  <p><strong>Expected:</strong>  </p>
  
  <pre><code>MyAwesomeReactNativeApp/
  ├── src/
  │   └── index.tsx
  └── build/
      └── index.js
  </code></pre>
  
  <p><strong>Got:</strong>  </p>
  
  <pre><code>MyAwesomeReactNativeApp/
  ├── src/
  │   └── index.tsx
  └── build/
      ├── src/
      │   └── index.js
      ├── index.android.js
      ├── index.ios.js
      └── __tests__/
  </code></pre>
  
  <p>The compiler complains:</p>
  
  <pre><code>error TS6059: File '[...]/__tests__/index.android.js' is not under 'rootDir' '[...]/src'. 'rootDir' is expected to contain all source files.
  error TS6059: File '[...]/__tests__/index.ios.js' is not under 'rootDir' '[...]/src'. 'rootDir' is expected to contain all source files.
  error TS6059: File '[...]/index.android.js' is not under 'rootDir' '[...]/src'. 'rootDir' is expected to contain all source files.
  error TS6059: File '[...]/index.ios.js' is not under 'rootDir' '[...]/src'. 'rootDir' is expected to contain all source files.
  </code></pre>
  
  <p>What am I doing wrong here?</p>
  
  <p>Thank you in advance!</p>