Update ch03-02-data-types.md

[narender2031]

Fix the number of scalar types

[carols10cents]

Sorry, you've changed "primary" to "five", so that now it reads "Rust has four five scalar types:"... and then the list following contains:

• integers
• floating-point numbers
• Booleans
• characters

which by my count is four, so the existing text is correct.

[narender2031]

@carols10cents Sorry by mistake i have edited the wrong character