title: VSCode shows TSLint errors only for opened file
body: <p>I have a project with this structure:</p>
  
  <pre><code>-src
  -dist
  -node_modules
  -gulpfile.js
  -tslint.json
  </code></pre>
  
  <p>My typescript files reside in src and are transpiled in a gulp task into dist folder. I've installed tslint locally and started with a plain tslint config: </p>
  
  <pre><code>{
      "rules": {
          "max-line-length": {
              "options": [120]
          }
      }
  }
  </code></pre>
  
  <p>Now, when I run tslint from a command line, I get warnings about all files in 'src' folder as expected. But VSCode highlights only the errors in currently opened file. The 'Problems' tab is getting filled only when I open a file with a tslint error.</p>
  
  <p>Do I need to add some configuration to VSCode launch.json? </p>