Fix deprecation warning in for using EmberApp.concatFiles
Fix deprecation warning in for using EmberApp.concatFiles

ember-fastboot/ember-cli-fastboot,tildeio/ember-cli-fastboot,kratiahuja/ember-cli-fastboot,kratiahuja/ember-cli-fastboot,ember-fastboot/ember-cli-fastboot,rwjblue/ember-cli-fastboot,josemarluedke/ember-cli-fastboot,tildeio/ember-cli-fastboot,josemarluedke/ember-cli-fastboot,rwjblue/ember-cli-fastboot