Update nlopes/slack vendor

vendor/github.com/nlopes/slack/webhooks.go

@@ -0,0 +1,33 @@
+package slack
+
+import (
+	"github.com/pkg/errors"
+	"net/http"
+	"bytes"
+	"encoding/json"
+)
+
+type WebhookMessage struct {
+	Text    		string 				`json:"text,omitempty"`
+	Attachments []Attachment	`json:"attachments,omitempty"`
+}
+
+func PostWebhook(url string, msg *WebhookMessage) error {
+	raw, err := json.Marshal(msg)
+
+	if err != nil {
+		return errors.Wrap(err, "marshal failed")
+	}
+
+	response, err := http.Post(url, "application/json", bytes.NewReader(raw));
+
+	if err != nil {
+		return errors.Wrap(err, "failed to post webhook")
+	}
+
+	if response.StatusCode != http.StatusOK {
+		return statusCodeError{Code: response.StatusCode, Status: response.Status}
+	}
+
+	return nil
+}