Documentation says go get -u but that is deprecated in module mode

` $ go get -u github.com/a8m/enter`
```
go: downloading golang.org/x/sys v0.0.0-20220224003255-dbe011f71a99
go get: installing executables with 'go get' in module mode is deprecated.
To adjust and download dependencies of the current module, use 'go get -d'.
To install using requirements of the current module, use 'go install'.
To install ignoring the current module, use 'go install' with a version,
like 'go install example.com/cmd@latest'.
For more information, see https://golang.org/doc/go-get-install-deprecation
or run 'go help get' or 'go help install'.
```