Fix r-devel failure

[hadley]

Kurt suggests it might be from a DESCRIPTION without a package field.

[hadley]

── Error ('test-build-home-authors.R:4:3'): authors page includes inst/AUTHORS ──
Error in `cit_info$`Date/Publication``: $ operator is invalid for atomic vectors
Backtrace:
    ▆
 1. ├─base::suppressMessages(build_citation_authors(pkg)) at test-build-home-authors.R:4:3
 2. │ └─base::withCallingHandlers(...)
 3. └─pkgdown:::build_citation_authors(pkg)
 4.   └─pkgdown:::data_citations(pkg) at pkgdown/R/build-home-authors.R:11:3
 5.     └─pkgdown:::citation_auto(pkg) at pkgdown/R/build-home-authors.R:255:3
 6.       └─cit_info$`Date/Publication` %||% Sys.time() at pkgdown/R/build-home-authors.R:279:3
── Error ('test-build-home.R:29:3'): .github files are copied and linked ───────
Error in `cit_info$`Date/Publication``: $ operator is invalid for atomic vectors
Backtrace:
    ▆
 1. ├─base::suppressMessages(build_home(pkg)) at test-build-home.R:29:3
 2. │ └─base::withCallingHandlers(...)
 3. └─pkgdown::build_home(pkg)
 4.   └─pkgdown:::build_citation_authors(pkg) at pkgdown/R/build-home.R:299:3
 5.     └─pkgdown:::data_citations(pkg) at pkgdown/R/build-home-authors.R:11:3
 6.       └─pkgdown:::citation_auto(pkg) at pkgdown/R/build-home-authors.R:255:3
 7.         └─cit_info$`Date/Publication` %||% Sys.time() at pkgdown/R/build-home-authors.R:279:3