Error handling. Vendoring

Signed-off-by: Ettore Dreucci <ettore.dreucci@gmail.com>

vendor/github.com/go-redis/redis/internal/util.go

@@ -0,0 +1,29 @@
+package internal
+
+import "github.com/go-redis/redis/internal/util"
+
+func ToLower(s string) string {
+	if isLower(s) {
+		return s
+	}
+
+	b := make([]byte, len(s))
+	for i := range b {
+		c := s[i]
+		if c >= 'A' && c <= 'Z' {
+			c += 'a' - 'A'
+		}
+		b[i] = c
+	}
+	return util.BytesToString(b)
+}
+
+func isLower(s string) bool {
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		if c >= 'A' && c <= 'Z' {
+			return false
+		}
+	}
+	return true
+}