Fix linter errors

[calderonsamuel]

Related issue

• Closes Fix lintr errors #198

Description of changes

• Multiple code changes for fixing multiple linting errors in the project
• New Github action for linting: https://github.com/r-lib/actions/blob/v2/examples/lint.yaml

For contributors

• I have added the relevant changes to the NEWS.md file
• I have added relevant tests or documentation with my changes

For reviewers

• [] Changes meet the acceptance criteria of the related issue
• [] The contribution follows style conventions and code of conduct
• [] Branch passes automated testing
• [] I have incremented the package version in the DESCRIPTION file before merging

[JamesHWade]

Thank you for fixing linting! That's great to have now.