There are a lot of characters in Japanese (and Chinese, of course) where the original form has two lines angled out like 八 on the top, and the simplified form (or commonly handwritten form, even when the letter has no official simplified form) has them angled the other way like /.
Kanji in the "common characters list" (常用漢字表) all have the V style simplification as far as I know. But 味噌 isn't one of those.
In fact, for me, when I type in みそ the only characters offered to me are 味噌. I don't get offered the one you have in Genki. My computer is 100% Japanese region with only Japanese input (ATOK) on it. Same with my phone, Japanese iPhone.
It must be a simplification (and I would not have any problem reading it in context). I'd suspect the usual "handwritten simplification" but it's interesting to see it there in a font.
So I looked it up in a character dictionary (旺文社漢字典）and your version IS in there! It's listed under 異体（いたい）, or "variant forms" of 噌、marked 俗字（ぞくじ）"popular/non-standard character."
But you should just keep in mind, that this 八 vs. V is a "thing" that happens, often a letter will have the 八 but even if not officially simplified, people will HANDWRITE with the V often, and then those letters that are officially simplified, get the V in the new form.
Sometimes this means there's interesting pairs:
利益（りえき）＝"profit" - notice the right hand character has the V, it's been simplfied from original 益 (which you can tell is the same basic form just with the lines flipped on the top, it's 八)
溢れる（あふれる）＝"to overflow" - notice this letter (currently used one!!) has the 八 on the top, in fact it's just the one above (old style) with 氵 on the left.
Because 溢 has no official simplified form (it's not on the common characters list) it doesn't have the lines up top flipped to V. And yet if you look at people's handwriting, lots of times they write it with V, so it's like the new 益 with 氵 on the left.
In fact I looked THAT one up in the same 旺文社漢字典 dictionary and whaddaya know, they list a letter "like the new 益 with 氵 on the left" (which I can't type easily here) and call that too, 俗字 ("popular/non-standard character").
...which is probably way more than you need, but just keep the "process" in the back of your mind, when you encounter some odd variations like this.