[BUG] Discord Webhook does not match expected format"

**Describe the bug**
Discord webhook does not match the expected format

**To Reproduce**
Steps to reproduce the behavior:
1. Go to config.yaml
notifications:
discord:
url: "https://discordapp.com/api/webhooks/{YourDiscord}" # [or url: "https://discord.com/api/webhooks/{YourDiscord}"]
notificationtypes:
- reacquire
- unknowndetected
- startrun
- endrun
2. run Checkrr

**Expected behavior**
Expect to send a Discord notification upon trigger

- OS: Docker container
- checkrr Version: 3.6.1

**Additional context**
time="level=warning msg="Webhook does not match expected format" Discord Connected=false Startup=true".

Proposed change:
regex.FindStringSubmatch(d.URL)
if matches != nil {
if len(matches) == 3 {

--> len(matches) == 3 to len(matches) == 4