fixing call url

GetThreddsURL("http://data.nodc.noaa.gov/thredds/catalog/ghrsst/L4/GLOB/
UKMO/OSTIA/catalog.xml")
GetThreddsURL("http://data.nodc.noaa.gov/thredds/catalog/ghrsst/L4/GLOB/
UKMO/OSTIA/")
GetThreddsURL("http://data.nodc.noaa.gov/thredds/catalog/ghrsst/L4/GLOB/
UKMO/OSTIA")

they are all valid requests now