attempt to use CORDOVA_VERSION=9 on travis to fix Xcode 11 build
attempt to use CORDOVA_VERSION=9 on travis to fix Xcode 11 build

BasqueVoIPMafia/cordova-plugin-iosrtc,BasqueVoIPMafia/cordova-plugin-iosrtc,eface2face/cordova-plugin-iosrtc,eface2face/cordova-plugin-iosrtc,BasqueVoIPMafia/cordova-plugin-iosrtc,eface2face/cordova-plugin-iosrtc,hit0907/cordova-plugin-iosrtc,hit0907/cordova-plugin-iosrtc,hit0907/cordova-plugin-iosrtc