Supervisor used graphic without crediting me
How to proceed from here?

You don't do anything. You did something small your supervisor asked for, and he used the figure that you made for him. 

It's very unusual for figures to be labeled with the name of the actual person that made it, and it would be a lot to expect this without asking / demanding this beforehand. Take the closest textbook and you'll find that indeed,  a lot of figures will be copied from publications and references are included. However, there will also be custom-made figures that don't have any note. And you can be quite sure these figures are not drawn by the authors themselves, but by their students or employees. 

There would probably also be no copyright implication, as this sounds like you just re-created some schematic figure and you just copied the idea, not the work itself.