This reverts commit f76652f379.
Go test no longer picks up the tests when run from the project root.
$ go test -v ./...
? github.com/matryer/moq [no test files]
testing: warning: no tests to run
PASS
ok github.com/matryer/moq/example (cached) [no tests to run]
? github.com/matryer/moq/generate [no test files]
Migrating to Go modules needs special handling for fake modules such as
github.com/matryer/buildconstraints.
