later 1.2.0 release candidate

[wch]

• [x] Create branch labelled rc-v1.2.0
• [x] Change the DESCRIPTION and NEWS on this branch to change the version number to the desired version for CRAN
• [x] Commit and push to the RC branch.
• [x] Build package
• [x] Do a sanity check by installing/testing the built package.
• [ ] Run R CMD check --as-cran pkg_version.tar.gz both locally and on win-builder. You can also use https://r-hub.github.io/rhub/.
• [x] Perform revdepcheck.
• [ ] Submit to CRAN
• [ ] If there are R CMD check warnings that are unavoidable, make sure to explain them in the comments.
• [ ] Tag release
• [ ] Merge tag into master
• [ ] Delete RC branch
• [ ] Rebuild and deploy website
• [ ] Create GitHub release, and copy NEWS items into release notes
• [ ] Bump version number
• [ ] Remove from Remotes in https://github.com/rstudio/shinycoreci DESCRIPTION file