title: grunt-tslint is not working at the watch task
body: <p>I'm working on an angular2 project and have included grunt-tslint to improve my code. The grunt task "tslint" and default grunt task is workink fine but when I include it to the watch task it's not linting. I tried to delete every other watch task but also not working. </p>
  
  <p>This are my versions:<br>
  grunt: v1.0.1<br>
  grunt-contrib-watch: 1.0.0<br>
  grunt-ts: v6.0.0-beta.3<br>
  grunt-tslint: 4.0.0</p>
  
  <p>And the grunt tasks:</p>
  
  <pre><code>module.exports = function (grunt) {
  
  grunt.initConfig({
  
      pkg: grunt.file.readJSON('package.json'),
      tslint: {
          options: {
              configuration: "tslint.json",
              force: false,
              fix: false
          },
          files: {
              src: ['app/**/*.ts']
          }
      },
      ts: {
          default : {
              src: ['app/**/*.ts'],
              outDir: 'outDir/app/',
              tsconfig: './tsconfig.json'
          }
      },
  
  watch: {
          tslint: {
              files: ['app/**/*.ts'],
              task: ['tslint']
          },
          ts: {
              files: ['app/**/*.ts'],
              tasks: ['ts']
          }
      }
  });
  
  grunt.loadNpmTasks('grunt-contrib-watch');
  grunt.loadNpmTasks('grunt-ts');
  grunt.loadNpmTasks('grunt-tslint');
  
  grunt.registerTask('default', [
      'ts', 'tslint'
  ]);
  
  grunt.registerTask('validate:ts', ['tslint']);
  </code></pre>
  
  <p>};</p>