Fixed offset and scale map on Python3

[jzavala-gonzalez]

Hey all, this looks great! I downloaded it earlier today and found that on Python3 the generated SVG didn't scale the stars' positions correctly. I found that the issue was on the map call around line 70 of the coord_calc.py file and fixed it by replacing it with a for loop with the contents of offset_and_scale instead. I'm not very sure how to suggest a commit so I just bring this up here. Best of luck! Awesome job it's great!