ci: update Chrome and Firefox in SauceLabs (angular#18808)

PR Close angular#18808

Author: marclaval

browser-providers.conf.js

@@ -41,10 +41,10 @@ var customLaunchers = {
   'DartiumWithWebPlatform':
       {base: 'Dartium', flags: ['--enable-experimental-web-platform-features']},
   'ChromeNoSandbox': {base: 'Chrome', flags: ['--no-sandbox']},
-  'SL_CHROME': {base: 'SauceLabs', browserName: 'chrome', version: '54'},
+  'SL_CHROME': {base: 'SauceLabs', browserName: 'chrome', version: '60'},
   'SL_CHROMEBETA': {base: 'SauceLabs', browserName: 'chrome', version: 'beta'},
   'SL_CHROMEDEV': {base: 'SauceLabs', browserName: 'chrome', version: 'dev'},
-  'SL_FIREFOX': {base: 'SauceLabs', browserName: 'firefox', version: '50'},
+  'SL_FIREFOX': {base: 'SauceLabs', browserName: 'firefox', version: '54'},
   'SL_FIREFOXBETA':
       {base: 'SauceLabs', platform: 'Windows 10', browserName: 'firefox', version: 'beta'},
   'SL_FIREFOXDEV':