Description

Please explain the changes you made here.

I fixed CI's error.

shellcheck comes standard with travis. Therefore, there is no need to install it explicitly.
With this patch, lint will work properly.

reference

https://github.com/koalaman/shellcheck/wiki/TravisCI

Requirements / Checklist

• Read the Contributing Guidelines
• Read or at least glanced at the FAQ
• Read or at least glanced at the Wiki
• Scripts execute without error (if necessary):
  • If any of the scripts were modified they have been tested and execute without error, e.g.:
    • ./font-patcher Inconsolata.otf --fontawesome --octicons --pomicons
    • ./gotta-patch-em-all-font-patcher\!.sh Hermit
• Extended the README and documentation if necessary, e.g. You added a new font please update the table

What does this Pull Request (PR) do?

Fix CI's error.

How should this be manually tested?

Nothing. Please see travis-ci's status.

Any background context you can provide?

https://travis-ci.org/github/kazukazuinaina/nerd-fonts/builds/699502908

It ispassing status in my fork repo.

What are the relevant tickets (if any)?

Screenshots (if appropriate or helpful)