Make Sass + ionic-starter-maps work out of the box

Hi,

   Currently, if you run yo-ionic, choose to use Sass, and then choose to use the maps starter template, when you attempt to run grunt serve on the app that is created you get an error. The reason is compass errors out when there are no sass files to compile. Simply adding a sass file to your styles directory will fix the error, but I could see it being confusing for beginners. Digging through the code, it looks like no main.sass is generated by generator-ionic if there is already a main.css from the starter template. My solution is to rename main.css to map.css here so the generator still creates the main.sass file. Anyway, not sure if this is the right solution, but wanted to make sure you were aware of the issue. Thanks!