Fail to parse date when testing a webhook with Gitlab

[cyrilc-pro]

When hitting the "test" button of a webhook in Gitlab, 14.4 the date format is slightly different and Froggit-Go is failing with the following error message: parsing time "2021-11-30T08:52:57.746Z" as "2006-01-02 15:04:05 MST": cannot parse "T08:52:57.746Z" as " "

[eyalbe4]

@cyrilc-pro, We'd gladly accept a pull request with a fix for this issue.