Provided, that provisions of this section prescribing the petition of freeholders as a condition precedent to the holding of any such election shall not apply to any incorporated municipality located in York County where the proceeds of the bonds to be authorized are used for any corporate purpose of such municipality. It is intended that the term "Incorporated municipality in York County" as used in this amendment shall mean all incorporated municipalities now existing or hereafter created, and as originally constituted or as afterwards altered following merger, annexation, or modification of corporate limits.