Feat/kerning number 4 and colon

[thierryc]

This is my first PR for the font itself.

I have added more space on the right in between the number four kern group and the colon kern group to balance well Black 4 shape.

Let me know if it is not the right way to contribute.

[rsms]

Nice. Could you please do the following:

1. rebase your branch onto latest rsms/inter@master (you may need to reapply your changes as the source structure changed)
2. provide sample screenshots of varying weights, italic and varying sizes (you can use the lab locally to do this: make build/fonts/var/Inter.var.woff2 && ./docs/lab/serve.py)

Thank you!