Update roxygen2 from CRAN email

[mikemahoney218]

From Kurt Hornik this morning:

Dear maintainer,

You have file 'geojsonio/man/geojsonio.Rd' with \docType{package},
likely intended as a package overview help file, but without the
appropriate PKGNAME-package \alias as per "Documenting packages" in
R-exts.

This seems to be the consequence of the breaking change

  Using @docType package no longer automatically adds a -package alias.
  Instead document _PACKAGE to get all the defaults for package
  documentation.

in roxygen2 7.0.0 (2019-11-12) having gone unnoticed, see
<https://github.com/r-lib/roxygen2/issues/1491>.

As explained in the issue, to get the desired PKGNAME-package \alias
back, you should either change to the new approach and document the new
special sentinel

  "_PACKAGE"

or manually add

  @aliases geojsonio-package

if remaining with the old approach.

Please fix in your master sources as appropriate, and submit a fixed
version of your package within the next few months.

Best,
-k