Update coinbase.json for ETH and LTC
Update coinbase.json for ETH and LTC

Coinbase added both ETH/USD and LTC/USD.
LeonidShamis/XChange,andre77/XChange,nopy/XChange,ww3456/XChange,Panchen/XChange,timmolter/XChange,douggie/XChange,evdubs/XChange,npomfret/XChange,gaborkolozsy/XChange,chrisrico/XChange,stachon/XChange,TSavo/XChange