all: clean up code, upgrade to modern Go

Signed-off-by: ddkwork

widget/editor.go

@@ -929,7 +929,7 @@ func (e *Editor) replace(start, end int, s string, addHistory bool) int {
 	if addHistory {
 		deleted := make([]rune, 0, replaceSize)
 		readPos := e.text.ByteOffset(start)
-		for i := 0; i < replaceSize; i++ {
+		for range replaceSize {
 			ru, s, _ := e.text.ReadRuneAt(int64(readPos))
 			readPos += int64(s)
 			deleted = append(deleted, ru)
@@ -1021,7 +1021,7 @@ func (e *Editor) deleteWord(distance int) (deletedRunes int) {
 		return r
 	}
 	runes := 1
-	for ii := 0; ii < words; ii++ {
+	for range words {
 		r := next(runes)
 		wantSpace := unicode.IsSpace(r)
 		for r := next(runes); unicode.IsSpace(r) == wantSpace && !atEnd(runes); r = next(runes) {