revert PostJSON, PutJSON

[yseto]

refer https://github.com/mackerelio/mackerel-client-go/releases/tag/v0.27.0

mackerel-client-go/mackerel.go

Lines 134 to 157 in b2e5f06

	// PostJSON shortcut method for posting json
	func (c *Client) PostJSON(path string, payload interface{}) (*http.Response, error) {
	return c.requestJSON("POST", path, payload)
	}
	// PutJSON shortcut method for putting json
	func (c *Client) PutJSON(path string, payload interface{}) (*http.Response, error) {
	return c.requestJSON("PUT", path, payload)
	}
	func (c *Client) requestJSON(method string, path string, payload interface{}) (*http.Response, error) {
	var body bytes.Buffer
	err := json.NewEncoder(&body).Encode(payload)
	if err != nil {
	return nil, err
	}
	req, err := http.NewRequest(method, c.urlFor(path).String(), &body)
	if err != nil {
	return nil, err
	}
	req.Header.Add("Content-Type", "application/json")
	return c.Request(req)
	}

[yseto]

thanks your review.