fix(vec): Correct typo in Vec macro

[giantcow]

Just a little type I noticed

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @marioidival (or someone else) soon.

[marioidival]

Hello @RyoshiKayo I appreciate you opening the PR. Your change is invalid because it includes a compiler error.

   Compiling playground v0.0.1 (/playground)
error[E0423]: expected value, found builtin type `i32`
 --> src/main.rs:7:23
  |
7 |     let mut xs = vec![i32, 2, 3];
  |                       ^^^ not a value
  |

This is the reason why I will be closing this PR