build: allow golangci-lint to use more than 1 core
build: allow golangci-lint to use more than 1 core

Since switching to `golangci-lint` we have set the `-j 1` flag, which
restricts the tool to using 1 CPU thread.

This PR removes the flag so `make check` takes less time on good
computers.

hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad