Build failures on 32bit architectures

Job #4826687641 failed for cbc3ef59:

    vss_test.go:184: 
        	Error Trace:	/volumes/builds/B3GuLyk7/1/kalilinux/packages/golang-go.dedis-kyber/debian/output/source_dir/_build/src/go.dedis.ch/kyber/share/vss/pedersen/vss_test.go:184
        	Error:      	Expected nil, but got: &errors.errorString{s:"Error while decoding field {Name:SecShare PkgPath: Type:*share.PriShare Tag: Offset:12 Index:[1] Anonymous:false}: Error while decoding field {Name:I PkgPath: Type:int Tag: Offset:0 Index:[0] Anonymous:false}: detected a 32bit machine, please use either int64 or int32"}