sb flag incorrectly aligned

[timobrembeck]

There is a small issue in the sb flag of the Solomon Islands in which the yellow line is horizontal instead of vertical. I'm sure this is an easy fix, however I am not well versed with svg code and gradients 🤪

Here is the current svg:

And here is the flag according to Wikipedia:

This ticket was first opened the upstream repository (jackiboy/flagpack#7), but since this is no longer maintained and the problem persists on my fork, I copied it into this repository as well.