Installation Error

when.i try run ```go get github.com/knrt10/asciiConvert```
i got error : 

I'm on MasOS
go version go1.14 darwin/amd64

``` /go/src/github.com/knrt10/asciiConvert/cmd/root.go:86:20: assignment mismatch: 3 variables but mimetype.DetectFile returns 2 values ```