The git repo of github.com/containerd/stargz-snapshotter now has two go.mod modules:
- github.com/containerd/stargz-snapshotter
- github.com/containerd/stargz-snapshotter/estargz
So we need to have the following `replace` directive in `go.mod`:
```
github.com/containerd/stargz-snapshotter/estargz => github.com/containerd/stargz-snapshotter/estargz <VERSION>
```
Otherwise `go mod tidy` fails with the following error:
```
go: github.com/containerd/stargz-snapshotter@v0.2.1-0.20201217071531-2b97b583765b requires
github.com/containerd/stargz-snapshotter/estargz@v0.0.0-00010101000000-000000000000: invalid version: unknown revision 000000000000
```
ref: https://github.com/containerd/stargz-snapshotter/pull/195
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>