ct_commodity_lookup Fails With All Caps Input

[ChrisMuir]

ct_commodity_lookup("halibut")
#> $halibut
#> [1] "030221 - Fish; halibut (reinhardtius hippoglossoides, hippoglossus hippoglossus, hippoglossus stenolepis), fresh or chilled (excluding fillets, livers, roes and other fish meat of heading no. 0304)"
#> [2] "030331 - Fish; halibut (reinhardtius hippoglossoides, hippoglossus hippoglossus, hippoglossus stenolepis), frozen (excluding fillets, livers, roes and other fish meat of heading no. 0304)"

ct_commodity_lookup("HALIBUT")
#> $HALIBUT
#> character(0)

#> Warning message:
#> There were no matching results found 

These two commodity lookup queries should return the same results.

This issue first came up in #5.