[email protected]: download url changed

[BradKnowles]

GitExtensions changed the format of the download URL from version 4.2.1.17611 to 5.0.0.17897.

I've pasted updated regex and autoupdate values below. Will try to get a PR in a bit later.

        "regex": "/v(?<tag>[\\d.]+)\/GitExtensions-Portable-(?<arch>x64)-([\\d.]+)-(?<commit>[\\w]+)\\.zip"
    },
    "autoupdate": {
        "url": "https://github.com/gitextensions/gitextensions/releases/download/v$matchTag/GitExtensions-Portable-$matchArch-$version-$matchCommit.zip"
    }