pre-Download of murSST in `add_griddap()` example so that example can run within CRAN Time limits
murSSTAn object of class griddap_nc (inherits from nc, data.frame) with 0 rows and 2 columns.
obtained using the `rerddap` command murSST <- griddap( 'jplMURSST41', latitude = c(22, 51), longitude = c(-140, -105), time = c('last', 'last'), fields = 'analysed_sst' )