use MetaCPAN::Client instead of deprecated MetaCPAN::API

hi,
MetaCPAN::API is deprecated and was replaced with an official client to MetaCPAN: MetaCPAN::Client.
to save you some trouble I tried to do the conversion for you.
this change is supposed to do the simple code change from the old to the new, though I can't test it as the t folder is empty.
please check that it works as expected before merging.
thanks,
Mickey