Change inclusive range operator to `..=`

[legends2k]

In 1. Basics ~ Matching inclusive range should be written ..=:

warning: `...` range patterns are deprecated
 --> src/main.rs:5:10
  |
5 |         0...3 => "small",
  |          ^^^ help: use `..=` for an inclusive range
  |
  = note: `#[warn(ellipsis_inclusive_range_patterns)]` on by default