Add escapes to 'to nuon' (#4964)

crates/nu-command/src/formats/to/nuon.rs

@@ -137,10 +137,15 @@ fn value_to_string(v: &Value, span: Span) -> Result<String, ShellError> {
             }
             Ok(format!("{{{}}}", collection.join(", ")))
         }
-        Value::String { val, .. } => Ok(format!("\"{}\"", val)),
+        Value::String { val, .. } => Ok(format!("\"{}\"", escape(val))),
     }
 }
 
+fn escape(input: &str) -> String {
+    let output = input.replace('\\', "\\\\");
+    output.replace('"', "\\\"")
+}
+
 fn to_nuon(call: &Call, input: PipelineData) -> Result<String, ShellError> {
     let v = input.into_value(call.head);