install failed with git error...

[jimiwills]

Jimis-iMac:~ jbwills$ brew cask install horndis
==> Downloading https://ghcr.io/v2/homebrew/portable-ruby/portable-ruby/blobs/sha256:b065e5e3783954f3e65d8d3a6377ca51649bfcfa21b356b0dd70490f74c6bd86
######################################################################## 100.0%
==> Pouring portable-ruby-2.6.3_2.yosemite.bottle.tar.gz
Updating Homebrew...
error: Not a valid ref: refs/remotes/origin/master
fatal: ambiguous argument 'refs/remotes/origin/master': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

it hung here.

system details:

Jimis-iMac:~ jbwills$ sw_vers -productVersion
10.12.6
Jimis-iMac:~ jbwills$ uname -a
Darwin Jimis-iMac 16.7.0 Darwin Kernel Version 16.7.0: Thu Jun 15 17:36:27 PDT 2017; root:xnu-3789.70.16~2/RELEASE_X86_64 x86_64