update comment of runtime/impl.rs

[sekisamu]

according to the code in function convert, the formula should be:

some_value = (1 + (v * diff) + (v * diff)^2 / 2)
new_weight = old_weight + some_value (instead of multiplying it)

[parity-cla-bot]

It looks like @hammeWang signed our Contributor License Agreement. 👍

Many thanks,

Parity Technologies CLA Bot

[kianenigma]

This was reported a while ago and I have to look into it one more time. Indeed the research page of w3f and the implementation diverge a bit. Since the implementation was co-authored with someone else and was a long time ago, I prefer double checking it one more time. I am suspicious of our implementation being slightly wrong, in which case the comment is correct and the code needs fixing.

related:
#2854
darwinia-network/darwinia#447

I'll try to check it shortly, please don't merge/approve in the meantime.

[kianenigma]

Fixed here #6334