Hold on, let the Japanese master do this. xD
Here we're having a little Japanese lesson, so enjoy.
The Japanese writing is the same.
It is, in fact, written in Romaji (the English version of Japanese, really. xD) is Iibui. (pronounced ee-bwee)
イ means i
ー also means I (in this case)
ブ means bu
イ means i
However what they do in Romaji is make it a little less confusing. E.g.,
キング is 'kingu'. But people (like me) are able to figure out that that says 'king'!
ランプ is 'rampu'. After some conversion, it's 'lamp'.
コンピューター is 'konpuutaa'. After some conversion, it's 'computer'.
ツタージャ is Snivy's Japanese name, 'Tsutaaja'. After some conversion, it can be called 'Tsutarja' (as Serebii did at Black and White's pre-release)
Do you see how you are able to convert it?
However, sometimes conversion can be different, but it would still mean the same thing. For example, 'ランプ' can be called 'ranpu' or 'rampu'. This is the same with Eevee. Eevee has many Romaji conversions that someone might change it to. Some examples:
They are all right.
Also, one example could also be 'Eevee', however it wouldn't be quite right.
So, to sum it all up, both conversions are right.
No need to be alarmed. :D
Hope I helped. :)
Source: My Japanese-filled brain ^-^