lib/classes/Variables.js/Variables/constructor
class Variables:  constructor(serverless) {
    this.serverless = serverless;
    this.service = this.serverless.service;

    this.overwriteSyntax = RegExp(/,/g);
    this.fileRefSyntax = RegExp(/^file\((~?[a-zA-Z0-9._\-/]+?)\)/g);
    this.envRefSyntax = RegExp(/^env:/g);
    this.optRefSyntax = RegExp(/^opt:/g);
    this.selfRefSyntax = RegExp(/^self:/g);
    this.cfRefSyntax = RegExp(/^cf:/g);
    this.s3RefSynax = RegExp(/^s3:(.+?)\/(.+)$/);
  }