Double quotes are garbled when notifying to Slack

## WHAT

Double quotes are garbled when notifying Slack.

When the result is as below,
```
max_capacity: "1" => "2"
```

it becomes as below
```
max_capacity: &#34;1&#34; => &#34;2&#34;
```

## WHY

Slack does not convert to HTML entities and only three: `&`, `<`, and `>`.
https://api.slack.com/docs/message-formatting#how_to_escape_characters
