Array types are formatted in non-standard way in type hints

[jplatte]

Thanks for ra! I quickly noticed a very minor thing when trying it out: With this code

let x = [0.0; 3];

I get a type hint like this:

let x: [f64;_] = [0.0; 3];

This is not how rustfmt would format this if there was a type annotation (actually, _ is not valid in that position, but this is true when using 3 instead in this example). It would add a space after the semicolon:

let x: [f64; _] = [0.0; 3];

[matklad]

closed by #2926