Use correct case for 'allowunsafeurl' in error (#34)
Use correct case for 'allowunsafeurl' in error (#34)

'AllowUnsafeURL' in googet.conf doesn't work because
go-yaml/yaml's Unmarshal() expects keys to be all
lowercase. The error message about unsafe repos was
therefore misleading. This change informs the user
of the correct key to put in googet.conf.
davegalos/googet,davegalos/googet,google/googet