fix: linter issue

megacheck, gosimple and unused has been deprecated and subsumed by
staticcheck. And staticcheck also has been upgraded. we need to update
code for the linter issue.

close: #2945

Signed-off-by: Wei Fu <fuweid89@gmail.com>

remotes/docker/auth.go

@@ -79,8 +79,8 @@ func init() {
 		var t octetType
 		isCtl := c <= 31 || c == 127
 		isChar := 0 <= c && c <= 127
-		isSeparator := strings.IndexRune(" \t\"(),/:;<=>?@[]\\{}", rune(c)) >= 0
-		if strings.IndexRune(" \t\r\n", rune(c)) >= 0 {
+		isSeparator := strings.ContainsRune(" \t\"(),/:;<=>?@[]\\{}", rune(c))
+		if strings.ContainsRune(" \t\r\n", rune(c)) {
 			t |= isSpace
 		}
 		if isChar && !isCtl && !isSeparator {