Error importing packages on Smart Contract - Hyperledger Fabric

Hi,

I've been trying to program a smart contract in GO language for SAP Hyperledger Fabric, but when I try to instantiate it, I've got the following error:

cannot find package "github.com/hyperledger/fabric/core/ledger" 

I'm trying to import the ledger package from GitHub but I'm unable to do it, I've got the same issue when I tried to import other packages as well. Is there any way to do it ? What are the packages supported from SAP and where can I find them ?

Thank you !