Update index.jsx,, changed expression from "." to "x" in multiplication

[Harshan-Nayak]

while multiplication , i changed symbol from "." to "x".

Checklist:

• I have read freeCodeCamp's contribution guidelines.
• My pull request has a descriptive title (not a vague title like Update index.md)

Closes #XXXXX

[naomi-lgbt]

Why the need for this change? * is a commonly used mathematical symbol for multiplication, to avoid confusion with x as a variable.

[Harshan-Nayak]

Why the need for this change? * is a commonly used mathematical symbol for multiplication, to avoid confusion with x as a variable.

In UI , The * symbol is shown as dot(.) , so to avoid confuion with dot(.) and multiplication , 'x' should be implemented

[naomi-lgbt]

I'm not sure those two are particularly confusing, but I'll let others weigh in. :3

[Harshan-Nayak]

I'm not sure those two are particularly confusing, but I'll let others weigh in. :3

In real world, generally we use dot(.) for decimals and 'x' for multiplication , so for better user experience it will be better to use "x", in our mobile or laptop on screen calculators we generally use 'x' as multiplying symbol.