refactor(cleancss): moved common config values to environment variables

Author: danbucholtz

config/cleancss.config.js

@@ -5,11 +5,11 @@ module.exports = {
   /**
    * sourceFileName: the file name of the src css file
    */
-  sourceFileName: 'main.css',
+  sourceFileName: process.env.IONIC_OUTPUT_CSS_FILE_NAME,
 
   /**
    * destFileName: the file name for the generated minified file
    */
-  destFileName: 'main.css'
+  destFileName: process.env.IONIC_OUTPUT_CSS_FILE_NAME
 
 };