[BUG]Context.ServeFile send 'application/wasm' with a wrong extra field

[rocket049]

Describe the bug
Context.ServeFile send 'application/wasm' with a wrong extra field

To Reproduce
Steps to reproduce the behavior:

app.Get("/{key:path}", func(ctx iris.Context){
   ...  //get filename :  xx.wasm
    ctx.ServeFile(filename, ctx.ClientSupportsGzip())
})

Expected behavior

The content-type must be 'application/wasm'.

But it will be 'application/wasm; charset=UTF-8' now.

The problem is FireFox72 will report error 'unsupported mime type'.

Otherwise, chrome can work well.

[kataras]

@rocket049 thanks for the report! It's fixed now.