Update Procfile to use TIMEOFF_ADDR
Update Procfile to use TIMEOFF_ADDR

The HTTP server port is now defined using the `TIMEOFF_ADDR` environment
variable.

Also, run `go build` rather than `go run` to ensure that both `main.go`
and `routes.go` are taken into account by the compiler; see:
https://github.com/golang/go/issues/5164

mattbostock/leavediary