Wikipedia has some background on the spelling: https://en.wikipedia.org/wiki/Jujutsu#Etymology

> Jujutsu is derived using the Hepburn romanization system. Before the first half of the 20th century, however, jiu-jitsu and ju-jitsu were preferred,

Supposed by who? Maybe it's supposed to be 柔術.

You guys are nitpicking on the name while I clicked the link seriously thinking it's cool and could help to shrink my bellyfat.