We'll use this to call the Windows ReplaceFile API for safe file
replacement when updating credentials.tf.json in "terraform login" and
"terraform logout".
This brings in a bugfix for analyzing variables inside relative traversal
expressions in HCL, and a cosmetic bugfix in cty for GoString of
cty.NullVal(cty.DynamicPseudoType).
This also updates some other packages, as a result of running "go get -u".
This includes a bugfix to the cty/msgpack package to ensure correct
decoding of unknown and null values.
This also includes updates to cty's dependencies.
Nomad was manually updated, so revert that to the version in master,
remove it from vendor.json and add it to the ignore list.
Update all packages that were in an unknown state to their latest master
commits.
Martin Atkins