Check and update app's version for both AppStore & Fir
######1.Add Channel in info.plist
Now we only support two channels "AppStore" or "Fir", no channel or other channel are ignored.
######2.Include library use CocoaPods pod 'VersionUpdate', '~> 1.0.2'
######3.Call this when app launch
let versionUpdate = VersionUpdate()
versionUpdate.addAppStoreChannelWithAppId("your app id on appstore")
versionUpdate.addFirChannelWithAppId("your app id on fir", token: "your koken on fir", downloadUrl: "http://fir.im/xxxxxx")
versionUpdate.checkUpdate()
######4.If there has new version,just show alert which you can ignore or go to update.
