issue building with go 1.11.3 and previous

9532c33cb8812a3a439858750fb792cb88d35495 is causing versions prior to go 1.11.4 to have issues requiring the module.

e.g. semaphore v1 has go 1.11.0 as latest version and builds fail with:
```
go build github.com/google/gofuzz: module requires Go 1.12
```

note: travis-ci hasn't tested the last 2 commits on master.
