isValid() {
    const schemaObj = require('fresh-resume-schema');
    validator = require('is-my-json-valid');
    const validate = validator( schemaObj, { // See Note [1].
      formats: { date: /^\d{4}(?:-(?:0[0-9]{1}|1[0-2]{1})(?:-[0-9]{2})?)?$/ }
    });
    const ret = validate(this);
    if (!ret) {
      this.imp = this.imp || { };
      this.imp.validationErrors = validate.errors;
    }
    return ret;
  }
Validate the sheet against the FRESH Resume schema.