old_contents: var gulp = require("gulp");
  var util = require("gulp-util");
  var rename = require("gulp-rename");
  var run_sequence = require("run-sequence");
  
  const PORT = process.env.PORT || 8080;
  
  gulp.task("prebuild", (callback) => {
      run_sequence("copy_index", callback);
  });
  
  gulp.task("build", (callback) => {
      run_sequence("prebuild", "webpack", callback);
  });
  
  gulp.task("dev", (callback) => {
      run_sequence("prebuild", "webpack_dev_server", callback);
  });
  
  gulp.task("copy_index", () => {
      return gulp.src("src/index.html").pipe(gulp.dest("build"));
  });
  
  gulp.task("webpack", (callback) => {
      var webpack = require("webpack");
      var config = require("./webpack.config");
      webpack(config, (err, stats) => {
          if (err) {
              throw new util.PluginError("webpack", err);
          }
          util.log("[webpack]", stats.toString({
              colors: true
          }));
          callback();
      });
  });
  
  gulp.task("webpack_dev_server", (callback) => {
      var webpack = require("webpack");
      var webpack_dev_server = require("webpack-dev-server");
      var config = require("./webpack.config");
      config.entry.app.unshift("webpack-dev-server/client?http://localhost:" + PORT + "/");
      var compiler = webpack(config);
      var server = new webpack_dev_server(compiler, {
          contentBase: "build",
          publicPath: config.output.publicPath,
          filename: config.output.filename,
          stats: { colors: true },
          historyApiFallback: true
      }).listen(PORT, "localhost", (err) => {
              if (err) {
                  throw new util.PluginError("webpack-dev-server", err);
              }
              callback();
          });
  });
  
new_contents: var gulp = require("gulp");
  var util = require("gulp-util");
  var rename = require("gulp-rename");
  var run_sequence = require("run-sequence");
  
  const PORT = process.env.PORT || 8080;
  
  gulp.task("prebuild", (callback) => {
      run_sequence("copy_index", callback);
  });
  
  gulp.task("build", (callback) => {
      run_sequence("prebuild", "webpack", callback);
  });
  
  gulp.task("dev", (callback) => {
      run_sequence("prebuild", "webpack_dev_server", callback);
  });
  
  gulp.task("copy_index", () => {
      return gulp.src("src/index.html").pipe(gulp.dest("build"));
  });
  
  gulp.task("webpack", (callback) => {
      var webpack = require("webpack");
      var config = require("./webpack.config");
      webpack(config, (err, stats) => {
          if (err) {
              throw new util.PluginError("webpack", err);
          }
          util.log("[webpack]", stats.toString({
              colors: true
          }));
          callback();
      });
  });
  
  gulp.task("webpack_dev_server", (callback) => {
      var webpack = require("webpack");
      var webpack_dev_server = require("webpack-dev-server");
      var config = require("./webpack.config");
      config.entry.app.unshift("webpack-dev-server/client?http://localhost:" + PORT + "/");
      var compiler = webpack(config);
      var server = new webpack_dev_server(compiler, {
          contentBase: "build",
          publicPath: config.output.publicPath,
          filename: config.output.filename,
          stats: { colors: true },
          historyApiFallback: true
      }).listen(PORT, "localhost", (err) => {
          if (err) {
              throw new util.PluginError("webpack-dev-server", err);
          }
          callback();
      });
  });
  
subject: Fix indentation