The latest Cordova-cli version is recommended.
And please install the plugin from the multiple_maps branch.
$> cordova --version
6.3.1 // At least 6.2.0 is good.
$> npm cache clean
$> cordova create myApp org.apache.cordova.myApp myApp
$> cd myApp
$> cordova platform add android
$> cordova platform add ios
// Add the SDK plugin at first with --nofetch option
$> cordova plugin add https://github.com/mapsplugin/cordova-plugin-googlemaps-sdk --nofetch
$> cordova plugin add https://github.com/mapsplugin/cordova-plugin-googlemaps#multiple_maps \
--variable API_KEY_FOR_ANDROID="<YOUR KEY>" \
--variable API_KEY_FOR_IOS="<YOUR KEY>" \
--nofetch