chore(e2e): fix end-to-end testing with the latest firefox (#224)

- installing the latest version of firefox should fix launching firefox with
  selenium standalone server 3.0.1
- set gulpfile to download the latest version of selenium standalone server

circle.yml

@@ -8,6 +8,13 @@ dependencies:
  - curl -L -o google-chrome.deb https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
  - sudo dpkg -i google-chrome.deb
 
+ override: 
+ # Install latest Firefox
+ # https://discuss.circleci.com/t/installing-the-latest-version-of-firefox-in-circleci/1347
+ - pip install mozdownload mozinstall
+ - mozdownload --version latest --destination firefox.tar.bz2
+ - mozinstall firefox.tar.bz2
+
 test:
  override:
  - npm run check_format

gulpfile.js

@@ -67,11 +67,11 @@ gulp.task('test:unit', ['format', 'build'], function(done) {
 var e2e_env = {headless: false, kvm: true};
 gulp.task('update', ['build'], function(done) {
  runSpawn(process.execPath, ['bin/webdriver-manager', 'update', '--android',
- '--android-accept-licenses', '--versions.standalone', '3.0.0-beta4'], done);
+ '--android-accept-licenses'], done)
 });
 gulp.task('start', ['build', 'shutdown'], function(done) {
  runSpawn(process.execPath, ['bin/webdriver-manager', 'start', '--detach', '--seleniumPort',
- '4444', '--android', '--appium-port', '4723', '--versions.standalone', '3.0.0-beta4',
+ '4444', '--android', '--appium-port', '4723', 
  '--quiet'].concat(e2e_env.headless ||
  !e2e_env.kvm ? ['--avds', 'none'] : []), done);
 });