Performance fix - unnecessary rune convertion on --ansi

> time cat /tmp/list | fzf-0.10.1-darwin_amd64 --ansi -fqwerty > /dev/null

    real    0m4.364s
    user    0m8.231s
    sys     0m0.820s

    > time cat /tmp/list | fzf --ansi -fqwerty > /dev/null

    real    0m4.624s
    user    0m5.755s
    sys     0m0.732s

src/reader.go

@@ -5,14 +5,13 @@ import (
 	"io"
 	"os"
 	"os/exec"
-	"unicode/utf8"
 
 	"github.com/junegunn/fzf/src/util"
 )
 
 // Reader reads from command or standard input
 type Reader struct {
-	pusher   func([]rune) bool
+	pusher   func([]byte) bool
 	eventBox *util.EventBox
 	delimNil bool
 }
@@ -42,21 +41,10 @@ func (r *Reader) feed(src io.Reader) {
 		// end in delim.
 		bytea, err := reader.ReadBytes(delim)
 		if len(bytea) > 0 {
-			runes := make([]rune, 0, len(bytea))
-			for i := 0; i < len(bytea); {
-				if bytea[i] < utf8.RuneSelf {
-					runes = append(runes, rune(bytea[i]))
-					i++
-				} else {
-					r, sz := utf8.DecodeRune(bytea[i:])
-					i += sz
-					runes = append(runes, r)
-				}
-			}
 			if err == nil {
-				runes = runes[:len(runes)-1]
+				bytea = bytea[:len(bytea)-1]
 			}
-			if r.pusher(runes) {
+			if r.pusher(bytea) {
 				r.eventBox.Set(EvtReadNew, nil)
 			}
 		}