[Executive power; election and terms of governor and lieutenant-governor]Section 1. The executive power shall be vested in the governor, who shall hold office for four years; the lieutenant-governor shall be chosen at the same time, and for the same term. The governor and lieutenant-governor shall be chosen at the general election held in the year nineteen hundred thirty-eight, and each fourth year thereafter. They shall be chosen jointly, by the casting by each voter of a single vote applicable to both offices, and the legislature by law shall provide for making such choice in such manner. The respective persons having the highest number of votes cast jointly for them for governor and lieutenant-governor respectively shall be elected.