Compatibility with ubuntu-18.04 runner

[cbandy]

When I ran this action in the following matrix, both jobs failed with the jq help text, jq - commandline JSON processor [version 1.5-1-a5b5cbe], followed by head: write error: Broken pipe.

  kubernetes-k3d:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        kubernetes: [latest, v1.18]
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-go@v2
        with: { go-version: 1.x }
      - uses: nolar/setup-k3d-k3s@v1
        with:
          version: ${{ matrix.kubernetes }}
          k3d-args: --no-lb

This PR fixes two things:

1. Every invocation of jq has a filter. The default of . came about in 1.6, apparently.
2. No more pipes. The GH bash runner enables pipefail but now the action behaves consistently without it.

Along the way, I replaced the temporary files with variables and here strings. Tested on Bash 3.2.57 (macOS Big Sur) and Bash 5.0.3 (debian buster).

[cbandy]

@nolar is there anything I can do to help with this? Thanks for looking.

[nolar]

I am terribly sorry for the one-month delay. This PR somehow slipped through my hands and I did't noticed it. I'll take a look now. Thanks for pinging me.

[nolar]

Released as v1.0.4 and v1 (a moving ref).

Thanks for this contribution!