switch to a less generic icon

const CACHE_NAME = 'static-cache-v17b';

const CACHE_NAME = 'static-cache-v18';

const FILES_TO_CACHE = [

  '/favicon.ico',

  '/offline.html',

  '/static/v17/css/materialize.min.css',

  '/static/v17/css/material-icons.css',

  '/static/v17/css/local.css',

  '/static/v17/fonts/MaterialIcons-Regular.woff2',

  '/static/v17/fonts/MaterialIcons-Regular.woff',

  '/static/v17/fonts/MaterialIcons-Regular.ttf',

  '/static/v17/js/jquery-3.4.1.min.js',

  '/static/v17/js/materialize.min.js',

  '/static/v17/js/travelynx-actions.min.js',

  '/static/v17/js/autocomplete.min.js',

  '/static/v17/js/geolocation.min.js',

  '/static/v18/css/materialize.min.css',

  '/static/v18/css/material-icons.css',

  '/static/v18/css/local.css',

  '/static/v18/fonts/MaterialIcons-Regular.woff2',

  '/static/v18/fonts/MaterialIcons-Regular.woff',

  '/static/v18/fonts/MaterialIcons-Regular.ttf',

  '/static/v18/js/jquery-3.4.1.min.js',

  '/static/v18/js/materialize.min.js',

  '/static/v18/js/travelynx-actions.min.js',

  '/static/v18/js/autocomplete.min.js',

  '/static/v18/js/geolocation.min.js',

];

self.addEventListener('install', (evt) => {

  font-family: 'Material Icons';

  font-style: normal;

  font-weight: 400;

  src: url(/static/v17/fonts/MaterialIcons-Regular.eot); /* For IE6-8 */

  src: url(/static/v18/fonts/MaterialIcons-Regular.eot); /* For IE6-8 */

  src: local('Material Icons'),

       local('MaterialIcons-Regular'),

       url(/static/v17/fonts/MaterialIcons-Regular.woff2) format('woff2'),

       url(/static/v17/fonts/MaterialIcons-Regular.woff) format('woff'),

       url(/static/v17/fonts/MaterialIcons-Regular.ttf) format('truetype');

       url(/static/v18/fonts/MaterialIcons-Regular.woff2) format('woff2'),

       url(/static/v18/fonts/MaterialIcons-Regular.woff) format('woff'),

       url(/static/v18/fonts/MaterialIcons-Regular.ttf) format('truetype');

}

.material-icons {