fix exists-sync deprecation by replacing with fs.existsSync
fix exists-sync deprecation by replacing with fs.existsSync

unchartedcode/ember-cli-mirage,unchartedcode/ember-cli-mirage,jherdman/ember-cli-mirage,makepanic/ember-cli-mirage,jherdman/ember-cli-mirage,jherdman/ember-cli-mirage,samselikoff/ember-cli-mirage,samselikoff/ember-cli-mirage,unchartedcode/ember-cli-mirage,samselikoff/ember-cli-mirage,samselikoff/ember-cli-mirage,makepanic/ember-cli-mirage,jherdman/ember-cli-mirage,unchartedcode/ember-cli-mirage