old_contents: import gulp from 'gulp';
   // import dotenv from 'dotenv';
  // import coverage from 'gulp-coverage';
  // import nodemon from 'gulp-nodemon';
  import jasmineNode from 'gulp-jasmine-node';
  import istanbulReport from 'gulp-istanbul-report';
  import coveralls from 'gulp-coveralls';
  import babel from 'gulp-babel';
  import istanbul from 'gulp-babel-istanbul';
  import injectModules from 'gulp-inject-modules';
  // Run app server
  /* gulp.task('serve', () =>
    nodemon({
      script: 'index.js',
      ext: 'js html',
      env: { NODE_ENV: process.env.NODE_ENV }
    })
  );*/
  
  gulp.task('transpile', () => {
    return gulp.src(['src/inverted-index.js', 'tests/inverted-index-tests.spec.js'])
    .pipe(babel({
      presets: ['es2015']
    }))
    .pipe(gulp.dest('dist/'));
  });
  
  // Generate coverage report
  gulp.task('test', () => {
    gulp.src('./coverage/coverage.json')
      .pipe(istanbulReport());
  });
  
  // Run tests
  gulp.task('run-test', ['transpile'], () => {
    gulp.src(['tests/inverted-index-tests.spec.js'])
      .pipe(jasmineNode());
  });
  
  // Generate coverage report
  gulp.task('coverage', (cb) => {
    gulp.src(['src/inverted-index.js', 'tests/inverted-index-tests.spec.js'])
      .pipe(istanbul())
      .pipe(istanbul.hookRequire())
      .on('finish', () => {
        gulp.src('tests/inverted-index-tests.spec.js')
        .pipe(babel())
        .pipe(injectModules())
        .pipe(jasmineNode())
        .pipe(istanbul.writeReports())
        .pipe(istanbul.enforceThresholds({ thresholds: { global: 50 } }))
        .on('end', cb);
      });
  });
  
  // Load code coverage to coveralls
  gulp.task('coverage', ['run-test'], () => {
    return gulp.src('coverage/lcov.info')
      .pipe(coveralls());
  });
  
  gulp.task('default', ['run-test', 'coverage', 'test']);
  
new_contents: import gulp from 'gulp';
   // import dotenv from 'dotenv';
  // import coverage from 'gulp-coverage';
  // import nodemon from 'gulp-nodemon';
  import jasmineNode from 'gulp-jasmine-node';
  import istanbulReport from 'gulp-istanbul-report';
  import coveralls from 'gulp-coveralls';
  import babel from 'gulp-babel';
  import istanbul from 'gulp-babel-istanbul';
  import injectModules from 'gulp-inject-modules';
  // Run app server
  /* gulp.task('serve', () =>
    nodemon({
      script: 'index.js',
      ext: 'js html',
      env: { NODE_ENV: process.env.NODE_ENV }
    })
  );*/
  
  gulp.task('transpile', () => {
    return gulp.src(['src/inverted-index.js', 'tests/inverted-index-tests.spec.js'])
    .pipe(babel({
      presets: ['es2015']
    }))
    .pipe(gulp.dest('dist/'));
  });
  
  // Generate coverage report
  gulp.task('test', () => {
    gulp.src('./coverage/coverage.json')
      .pipe(istanbulReport());
  });
  
  // Run tests
  gulp.task('run-test', ['transpile'], () => {
    gulp.src(['tests/inverted-index-tests.spec.js'])
      .pipe(jasmineNode());
  });
  
  // Generate coverage report
  gulp.task('coverage', (cb) => {
    gulp.src(['src/inverted-index.js', 'tests/inverted-index-tests.spec.js'])
      .pipe(istanbul())
      .pipe(istanbul.hookRequire())
      .on('finish', () => {
        gulp.src('tests/inverted-index-tests.spec.js')
        .pipe(babel())
        .pipe(injectModules())
        .pipe(jasmineNode())
        .pipe(istanbul.writeReports())
        .pipe(istanbul.enforceThresholds({ thresholds: { global: 50 } }))
        .on('end', cb);
      });
  });
  
  // Load code coverage to coveralls
  gulp.task('coveralls', ['run-test'], () => {
    return gulp.src('coverage/lcov.info')
      .pipe(coveralls());
  });
  
  gulp.task('default', ['run-test', 'coverage', 'coveralls', 'test']);
  
subject: Update gulpfile