Fix new roxygen2 warning about single line aliases

[jgabry]

Submission Checklist

• Run unit tests
• Declare copyright holder and agree to license (see below)

Summary

The new version of roxygen2 throws a warning if @aliases is more than one line. The solution is to use multiple @aliases tags.

Copyright and Licensing

Please list the copyright holder for the work you are submitting
(this will be you or your assignee, such as a university or company):
Jonah Gabry

By submitting this pull request, the copyright holder is agreeing to
license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.24%. Comparing base (73f0d4c) to head (7959355).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1188      +/-   ##
==========================================
+ Coverage   91.21%   91.24%   +0.03%     
==========================================
  Files          15       15              
  Lines        6121     6125       +4     
==========================================
+ Hits         5583     5589       +6     
+ Misses        538      536       -2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.