devtools v2.0.1

This is a minor release mainly fixing bugs which snuck through in the devtools
2.0.0 release.

• install() now correctly passes the upgrade parameter to
  remotes::install_deps() (@Paxanator, #1898).

• install_deps() now again works from any directory within a package (#1905)

• Add a RStudio addin for test_coverage().

• All tests which use remote resources are now skipped on CRAN, to avoid
  spurious failures