[semver:patch] Remove references to outdated job

[bharatr21]

Checklist

• [ ] All new jobs, commands, executors, parameters have descriptions
• [ ] Examples have been added for any significant new features
• [x] README has been updated, if necessary

Motivation, issues

This fixes #99 and removes references to the (now outdated) job orb-tools/shellcheck since it has moved into its own orb.

Description

[bharatr21]

If you don't mind and it doesn't take a lot of effort, can you please mark this PR as eligible for Hacktoberfest 2020?

[gmemstr]

@Bharat123rox I have added "Hacktoberfest" to the repository's topics, which should make this PR eligible :)

[bharatr21]

Thanks @gmemstr ! 🎉