Update the examples for E0191

[mu001999]

Location

https://doc.rust-lang.org/error_codes/E0191.html

Trait objects need to have all associated types specified. Please verify that all associated types of the trait were specified and the correct trait was used. Example:

trait Trait {
    type Bar;
}

type Foo = Trait<Bar=i32>; // ok!

Summary

But according to E0782, trait objects must include the dyn keyword:

error[[E0782]](https://doc.rust-lang.org/stable/error_codes/E0782.html): trait objects must include the `dyn` keyword
 --> src/lib.rs:5:12
  |
5 | type Foo = Trait<Bar=i32>; // ok!
  |            ^^^^^^^^^^^^^^
  |
help: add `dyn` keyword before this trait
  |
5 | type Foo = dyn Trait<Bar=i32>; // ok!
  |            +++

For more information about this error, try `rustc --explain E0782`.
error: could not compile `playground` (lib) due to previous error

I think the examples for E0191 should be updated.