It appears something has changed, possibly external, and all of the macOS builds are failing (including nightly)
./installpsh-osx.sh: line 99: [: missing `]'
\n*** Installing PowerShell Core for osx...
Howebrew is already installed, skipping...
Installing cask...
Updating Homebrew...
==> Downloading https://homebrew.bintray.com/bottles-portable/portable-ruby-2.3.3.leopard_64.bottle.1.tar.gz
######################################################################## 100.0%
==> Pouring portable-ruby-2.3.3.leopard_64.bottle.1.tar.gz
/usr/local/Homebrew/Library/Homebrew/brew.rb:12:in `<main>': Homebrew must be run under Ruby 2.3! (RuntimeError)
ERROR: Cask failed to install! Cannot install powershell...
The command "./install-powershell.sh" failed and exited with 2 during .
Also, the nightly badge for Travis CI macOS reports success when it clearly failed.