If I follow this steps to create a new app:
Rubens-MacBook-Pro:~ rlopez$ npm install -g cordova ionic Rubens-MacBook-Pro:~ rlopez$ ionic start myApp tabs Rubens-
For those who gets similar error after updating Android Studio to version 3.x, you can run the following command to fix it:
sudo chmod 755 /Applications/Android\ Studio.app/Contents/gradle/gradle-4.1/bin/gradle
Hopefully it helps!