feat(sync): add min sync interval time detect
feat(sync): add min sync interval time detect

Forbidden some guy write `config.syncInterval = 1` to let sync too fast.

Closes #486

marvinlee/cnpmjs.org,chinakids/cnpmjs.org,chinakids/cnpmjs.org,limianwang/cnpmjs.org,irachex/cnpmjs.org,marvinlee/cnpmjs.org,irachex/cnpmjs.org,limianwang/cnpmjs.org,chinakids/cnpmjs.org,yufi113/cnpmjs.org,yufi113/cnpmjs.org,marvinlee/cnpmjs.org,yufi113/cnpmjs.org,limianwang/cnpmjs.org,irachex/cnpmjs.org