improve escaping when colon in string

yaml/pretty/util.go

@@ -65,7 +65,7 @@ func isZero(v interface{}) bool {
 
 func isQuoted(b rune) bool {
 	switch b {
-	case ':', '#', ',', '[', ']', '{', '}', '&', '*', '!', '|', '>', '\'', '"', '%', '@', '`':
+	case '#', ',', '[', ']', '{', '}', '&', '*', '!', '|', '>', '\'', '"', '%', '@', '`':
 		return true
 	case '\a', '\b', '\f', '\n', '\r', '\t', '\v':
 		return true

yaml/pretty/writer.go

@@ -195,11 +195,17 @@ func writeEncode(w writer, v string) {
 		w.WriteByte('"')
 		return
 	}
+	var prev rune
 	for _, b := range v {
 		if isQuoted(b) {
 			fmt.Fprintf(w, "%q", v)
 			return
 		}
+		if b == ' ' && prev == ':' {
+			fmt.Fprintf(w, "%q", v)
+			return
+		}
+		prev = b
 	}
 	w.WriteString(v)
 }