Add Content-Type header for non-GET HTTP requests + rename function for more accuracy

src/grafana/client.go

 	authHeader := fmt.Sprintf("Bearer %s", c.APIKey)
 	req.Header.Add("Authorization", authHeader)
 
+	if method != "GET" {
+		req.Header.Add("Content-Type", "application/json")
+	}
+
 	resp, err := c.httpClient.Do(req)
 	if err != nil {
 		return nil, err

src/grafana/dashboards.go

 	return
 }
 
-func (c *Client) UpdateDashboard(slug string, contentJSON []byte) (err error) {
+func (c *Client) CreateOrUpdateDashboard(slug string, contentJSON []byte) (err error) {
 	reqBody := dbUpdateRequest{
 		Dashboard: rawJSON(contentJSON),
 		Overwrite: false,

src/pusher/webhook.go

 	// Remove the .json part
 	slug := strings.Split(filename, ".json")[0]
 
-	return grafanaClient.UpdateDashboard(slug, fileContent)
+	return grafanaClient.CreateOrUpdateDashboard(slug, fileContent)
 }