[pkg] update go.mod

go.mod

@@ -29,7 +29,6 @@ require (
 	github.com/stretchr/objx v0.2.0 // indirect
 	github.com/stretchr/testify v1.4.0 // indirect
 	golang.org/x/crypto v0.0.0-20191105034135-c7e5f84aec59 // indirect
-	golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e // indirect
 	golang.org/x/sys v0.0.0-20200212091648-12a6c2dcc1e4
 	golang.org/x/text v0.3.2
 	golang.org/x/tools v0.0.0-20200427153019-a90b7300be7c // indirect