运行此命令时：
ionic cordova platform add ios
发生错误：
> cordova platform add ios --save
Using cordova-fetch for cordova-ios@~4.5.4
Adding ios project...
iOS project created with cordova-ios@4.5.5
Installing "cordova-plugin-actionsheet" for ios
Installing "cordova-plugin-advanced-http" for ios
Plugin dependency "cordova-plugin-file@6.0.1" already fetched, using that version.
Installing "cordova-plugin-file" for ios
Installing "cordova-plugin-camera" for ios
Installing "cordova-plugin-datepicker" for ios
Installing "cordova-plugin-document-viewer" for ios
Plugin "cordova-plugin-file" already installed on ios. Making it top-level.
Installing "cordova-plugin-file-transfer" for ios
Plugin dependency "cordova-plugin-file@6.0.1" already fetched, using that version.
Dependent plugin "cordova-plugin-file" already installed on ios.
Installing "cordova-plugin-filepath" for ios
Installing "cordova-plugin-firebase" for ios
Installing "cordova-plugin-geolocation" for ios
Installing "cordova-plugin-googlemaps" for ios
Failed to install 'cordova-plugin-googlemaps': undefined
CordovaError: Promise rejected with non-error:
at cli.catch.err (/usr/local/lib/node_modules/cordova/bin/cordova:30:15)
at <anonymous>
at process._tickCallback (internal/process/next_tick.js:189:7)
[ERROR] An error occurred while running subprocess cordova.
离子信息
Ionic:
ionic (Ionic CLI) : 4.6.0 (/usr/local/lib/node_modules/ionic)
Ionic Framework : ionic-angular 3.9.2
@ionic/app-scripts : 3.1.0
Cordova:
cordova (Cordova CLI) : 8.1.2 (cordova-lib@8.1.1)
Cordova Platforms : android 7.1.4, ios 4.5.5
Cordova Plugins : cordova-plugin-ionic-keyboard 2.1.3, cordova-plugin-ionic-webview 1.2.1, (and 19 other plugins)
System:
NodeJS : v8.12.0 (/usr/local/bin/node)
npm : 6.4.1
OS : macOS Sierra
Xcode : Xcode 9.1 Build version 9B55
复制步骤：
sudo npm缓存清除--force
sudo离子cordova平台rm ios
sudo离子cordova平台添加ios
https://github.com/mapsplugin/cordova-plugin-googlemaps/issues/1435