ugrep shoud use byte based column number

Hi, Thanks your working. I notice that ugrep's column number is not same as grep or ag, rg etc.

```
あいう
```


```
$ rg --vimgrep い file.txt
file.txt:1:4:あいう
```

```
$ ag --vimgrep い file.txt
file.txt:1:4:あいう
```

```
$ ugrep -H -n -k い file.txt
file.txt:1:2:あいう
```

ugrep seems to output unicode character based column number.