sg: fails with unclear errors when running sg on old (unsupported) go versions

Created by: jhchabran

Context: https://sourcegraph-community.slack.com/archives/C02BG0M0ZJ7/p1634296034018800

The person is running an old go version, 1.10, and was facing odd errors related to Go modules when trying to compile the code.

Should we check the Go version in sg doctor or before running commands?