Fix GBrowse about url

[scottcain]

The GBrowse url used (gbrowse.org) isn't associated with GBrowse, and is defunct anyway. A better url is for the gmod.org wiki page for GBrowse

[osallou]

about.license field is not in spdx list: https://spdx.org/licenses/, if it is a typo error, please fix it. If this is not a standard license, then ignore this message.

[osallou]

Found a biotools entry matching the software name (https://bio.tools/gbrowse), if this is the same software, please add the extra.identifier.biotools label to your Dockerfile