uiucthemes 0.3.1

CHANGES

• Fixed citation_package = 'none' deprecation warning by changing
  to citation_package = 'default' (thanks for the report @noejn2, #21)
• Bumped the dependency requirements to rmarkdown 2.2 and xaringan 0.16.0.

DOCUMENTATION

• Re-built documentation under roxygen2 7.1.0
• Modernized the README file

DEPLOYMENT

• Switched from using TravisCI to GitHub Actions for continuous integration.