Ask yes or no if the screenshot was too small.

Previously this was retry or abort but those are less clear answers to
the question posed, "Try again?"

doomcc/ss.py

@@ -23,7 +23,7 @@ class SS(doomcc.doom_base.WadMap):
         with wand.image.Image(width=width, height=height, pseudo="x:") as img:
             img.reset_coords()
             if img.width < width or img.height < height:
-                if not messagebox.askretrycancel(
+                if not messagebox.askyesno(
                     title="Doom Command Center",
                     message=f"Image too small ({img.width}x{img.height})."
                     + "Try again?",