update the master branch to the latest

test/unit/karma.conf.js

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+// This is a karma config file. For more details see
+//   http://karma-runner.github.io/0.13/config/configuration-file.html
+// we are also using it with karma-webpack
+//   https://github.com/webpack/karma-webpack
+
+var webpackConfig = require('../../build/webpack.test.config.js');
+
+module.exports = function (config) {
+  config.set({
+    // to run in additional browsers:
+    // 1. install corresponding karma launcher
+    //    http://karma-runner.github.io/0.13/config/browsers.html
+    // 2. add it to the `browsers` array below.
+    browsers: ['ChromeHeadless'],
+    frameworks: ['mocha', 'sinon-chai'],
+    reporters: ['spec', 'coverage'],
+    files: ['./index.js'],
+    preprocessors: {
+      './index.js': ['webpack', 'sourcemap']
+    },
+    webpack: webpackConfig,
+    webpackMiddleware: {
+      noInfo: true,
+    },
+    coverageReporter: {
+      dir: './coverage',
+      reporters: [
+        { type: 'lcov', subdir: '.' },
+        { type: 'text-summary' },
+      ]
+    },
+  });
+};