My house is about 35 years old, and had two prong outlets. I pulled a couple out, and found the outlets were installed in a metal box. There was a ground wire, but it was grounded to the metal receptacle box and not the outlet. The ground wire looked a little smaller than the other wires. I installed a three prong outlet by connecting the ground wire from the wiring to the receptacle. I used the green wirenuts with the hole through the end to add a ground from the wirenut to the metal receptacle box. Was this the proper way to upgrade the outlets?