How to re-tension front derailleur cable Bike is a mid 80s Miyata with early Shimano 105 components. It's a 10 speed, 5 speed cog and 2 chain rings. 

I recently had my front derailleur set up again by a good mechanic after it stopped shifting at all. He reinstalled the derailleur to height/angle, adjusted the limits, and installed a new cable. It shifted great for a few days, super fluid and quick. Now it has trouble traveling far enough to reach the larger chain ring and I feel like the shift cable stretched a bit and needs to be re-tensioned. 

Is it likely the shift cable needs to be re-tensioned? Or the limits need to be readjusted?
Agree with others here - cables stretch only slightly, requiring one or two clicks/half turns of whatever barrel adjuster, either typically next to the headtube, or for the rear also where the cable meets the derailleur body. More than that, implies the cable actually slipped because the nut clamping it at the derailleur wasn't tightened enough.
  These are not complex issues, and every cyclist should learn how to at least make these basic adjustments, on principle to be more self-reliant, and also to free yourself from constant, costly, inconvenient trips to the shop. That said, the shop that did all the work should definitely follow up on what appears to be related to their work. Cables can also not be seated fully in the frame points etc. so another possibility exists there.