message: Fix isSyncable signature
diff: @@ -12,7 +12,7 @@ export const SYNCABLE = '__syncable__';
  * @param {SourceClass} source
  * @returns
  */
  -export function isSyncable(source: SourceClass) {
  +export function isSyncable(source: Source) {
  return !!source[SYNCABLE];
  }
  