update_plugin.sh: make script faster and fix syntax

[PhillipSz]

fix syntax: you can not use [ == ]; it's = or [[ == ]] or [[ = ]](both bash/zsh only). It does only work because bash corrects your mistake.

using & should make the script faster.

Everything works now and it's 2 sec's faster, except the tpm update. I don't know what the problem so please help me here.

If no one can help we must drop this PR.

Thanks.

[bruno-]

Hi, thank you for your work on this.
Unfortunately I still didn't look into this. Hopefully I'll find some time soon.
Thanks for the patience.

[NHDaly]

(It might be easier if you break this into two separate PRs. It seems pretty easy to approve the small change to the [[ == ]] syntax. That way the parallelization PR can be reviewed on its own. Cool idea though!)