GitLabWebhook.parsePushEvent method panics

[pavelmemory]

Describe the bug
Method parsePushEvent of the GitLabWebhook type panics in case there are no commits related to the event.
The actual code that causes the issue Timestamp: event.Commits[0].Timestamp.Local().Unix(),

Expected behavior
No panic to be generated.

• Froggit-Go version: https://github.com/jfrog/froggit-go/releases/tag/v1.0.0
• Operating system:

Additional context
Add any other context about the problem here.

[eyalbe4]

Thanks for reporting this issue @pavelmemory.
If you're able to contribute the fix for this issue, we'd truly appreciate it.