code: function(/*context*/) {
          this.log('rsync assets from ' + this.readConfig('source') + '…');
          var rsync = this.command();
          return new Promise(function(resolve, reject) {
            rsync.execute(function(error, code, cmd) {
              this.log('cmd: ' + cmd);
              if (error) {
                this.log(error);
                reject(new SilentError(error));
              } else {
                resolve();
              }
            }.bind(this), function(data) {
              this.log(data);
            }.bind(this));
          }.bind(this));
        }
docs: requiredConfig: ['source', 'destination'],