chore(test): update to iOS 8.4
chore(test): update to iOS 8.4

https://wiki.saucelabs.com/display/DOCS/2016/06/20/30-Day+EOL+Notice+for+iOS+5.1%2C+6.0%2C+6.1%2C+8.0

leeyeh/js-realtime-sdk,leeyeh/js-realtime-sdk,leancloud/js-realtime-sdk,leeyeh/js-realtime-sdk,leancloud/js-realtime-sdk