vagrant: darwin: add zstd

Vagrantfile

@@ -82,6 +82,7 @@ def packages_darwin
     ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
     brew update
     brew install openssl
+    brew install zstd
     brew install lz4
     brew install xz  # required for python lzma module
     brew install fakeroot