Fix missing quotation for dashes

Ref: homeport/dyff#342

Make sure to quote the dash in a string.

Author: HeavyWombat

output_yaml.go

@@ -362,6 +362,11 @@ func needsQuotes(node *yamlv3.Node) bool {
 		}
 	}
 
+	// check if strings starts with a dash
+	if strings.HasPrefix(node.Value, "-") {
+		return true
+	}
+
 	// check if string contains special characters
 	return strings.ContainsAny(node.Value, " *&:,")
 }

output_yaml_test.go

@@ -372,6 +372,7 @@ data:
   bar: true
   and: null
   but: "null"
+  dash: "-"
 `)
 
 			expected := `---
@@ -380,6 +381,7 @@ data:
   bar: true
   and: null
   but: "null"
+  dash: "-"
 `
 
 			var node yamlv3.Node