pythagorean-triplets: Fix maths notation in instructions (#1808)
pythagorean-triplets: Fix maths notation in instructions (#1808)

`**` is not commonly used for exponentiation. I went with `²` but `^` would also be a more common choice than `**`. In v3, this should probably be updated to use Mathjax/KaTeX notation instead. (see https://github.com/exercism/website/issues/476)
petertseng/x-common,petertseng/x-common,exercism/x-common,jmluy/x-common,jmluy/x-common,exercism/x-common,jmluy/x-common