am trying to install wekan on ubuntu but when i do 

```
sudo snap install wekan

```

i get certificates warning 

```
> - Download snap "core" (6531) from channel "stable" (Get https://fastly.cdn.snapcraft.io/download-origin/fastly/99T7MUlRhtI3U0QFgl5mXXESAiSwt776_6531.snap?token=1552986000_f5f9bd27ddd6a5fcdb342af604507b93bfd50383:
> x509: certificate has expired or is not yet valid)

```

so i wonder how to bypass the certificates check i know with wget we use --no-check-certificate flag to bypass certificates check so i wonder what is the flag for snap