[iOS] fix fastlane-plugin-firebase_app_distribution undefined

if fastlane add_plugin dose not work

[!] Could not find lane 'ios firebase_app_distribution'. Available lanes: ios release_dev, ios release_beta, ios release_prod, ios pre_build, ios increment_marketing_version, ios build, ios upload_to_firebase, ios upload_to_appstoreconnect, ios upload_to_crash

try below solution

// gemspec of firebase fastlane plugin 
// https://github.com/fastlane/fastlane-plugin-firebase_app_distribution/blob/master/fastlane-plugin-firebase_app_distribution.gemspec

$vi Gemfile
// add plugin
gem "fastlane-plugin-firebase_app_distribution" 

$bundle update

Using fastlane 2.167.0
Fetching fastlane-plugin-firebase_app_distribution 0.2.4
Installing fastlane-plugin-firebase_app_distribution 0.2.4

...
// then add plugin
$fastlane add_plugin firebase_app_distribution

// or update plugins
$fastlane update_plugins

References

https://stackoverflow.com/questions/60783449/how-to-fix-fastlane-plugin-firebase-app-distribution-undefined