title: Use of reserved word 'class' with karma and webpack
body: <p>I'm building a project with angularJS in ES6.</p>
  
  <p>I'm trying to config karma test runner and coverage with istanbul.</p>
  
  <p>When I try to lauch unit test with Karma, I've following error : </p>
  
  <pre><code>Use of reserved word 'class'
  </code></pre>
  
  <p>This is my karma config file : </p>
  
  <pre><code>var path = require('path');
  
  module.exports = function (config) {
      config.set({
  
          basePath: '',
  
          plugins: [
              'karma-coverage',
              'karma-jasmine',
              'karma-phantomjs-launcher',
              'karma-webpack',
              'karma-coverage-istanbul-reporter'
          ],
  
          frameworks: ['jasmine'],
  
          files: [
              'tests/index.js'
          ],
  
          preprocessors: {
              'tests/index.js': 'webpack'
          },
  
          webpack: {
              module: {
                  rules: [{
                      test   : /\.js$/,
                      use    : {
                          loader: 'istanbul-instrumenter-loader',
                          query : {
                              esModules: true
                          }
                      },
                      include: path.resolve('src/')
                  }, {
                      test: /\.html$/, loaders: ["html-loader"]
                  }, {
                      test: /\.less$/,
                      use : [{
                          loader: "style-loader"
                      }, {
                          loader: "css-loader"
                      }, {
                          loader: "less-loader"
                      }]
                  }, {
                      test  : /\.woff($|\?)|\.woff2($|\?)|\.ttf($|\?)|\.eot($|\?)|\.svg($|\?)/,
                      loader: 'url-loader'
                  }]
              }
          },
  
          reporters: ['progress', 'coverage-istanbul'],
  
          coverageIstanbulReporter: {
              reports              : ['text-summary'],
              fixWebpackSourcePaths: true
          },
  
          port       : 9876,
          colors     : true,
          logLevel   : config.LOG_INFO,
          autoWatch  : true,
          browsers   : ['PhantomJS'],
          singleRun  : true,
          concurrency: Infinity,
      })
  };
  </code></pre>
  
  <p>And this is my <code>tests/index.js</code> file</p>
  
  <pre><code>// requires all tests in `project/test/src/components/**/index.js`
  const tests = require.context('./specs/', true, /index\.js$/);
  tests.keys().forEach(tests);
  
  // requires all components in `project/src/components/**/index.js`
  const components = require.context('../src/', true, /\.js$/);
  components.keys().forEach(components);
  </code></pre>
  
  <p>Did I miss something ?</p>
  
  <p>Thanks.</p>