(ios) fix build errors caused with cordova-ios@7 due to CDVCommandDel

[ItsasoAguirre]

Pull request guide

Thank you for considering to improve this cordova-plugin-googlemaps.

When you create a pull request, please make it to multiple_maps branch instead of master branch.

Because the multiple_maps branch is edge version.

Thank you for your understanding.

[GitToTheHub]

Hi, could you make a branch for this fix in your repo?

Thanks