Fix typo in README.md

[kirkster96]

Proposed changes

This PR addresses Issue: [Link to Github issue within https://github.com/zowe/zlux/issues if any]

This PR depends upon the following PRs:

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

PR Checklist

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• If the changes in this PR are meant for the next release / mainline, this PR targets the "staging" branch.
• My code follows the style guidelines of this project (see: Contributing guideline)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• New and existing unit tests pass locally with my changes
• video or image is included if visual changes are made
• Relevant update to CHANGELOG.md
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works, or describe a test method below

Testing

Further comments