Seems like somehow googlemaps devDependencies didn’t install when you ran npm install. Run following to install devDependencies of the project as mentioned in https://github.com/aggarwalankush/ionic2-mosum/blob/master/package.json#L30
npm install @ionic/app-scripts@0.0.48 typescript@2.0.9 @types/googlemaps@3.25.36 @types/lodash@4.14.38 @types/moment-timezone@0.2.32
For publishing, see Publish Ionic app