Cirrus: Add workaround for Homebrew issue
See also:
@@ -150,6 +150,7 @@ mac_task:
brew install checkbashisms || >&2 printf 'Warning: Unable to install `checkbashims`\n'
- | # Start D-Bus session bus
brew tap homebrew/services
+ brew update # Work around for [Homebrew Services issue 206](https://github.com/Homebrew/homebrew-services/issues/206)
brew services start dbus
- | # Install Python
brew install python@2; brew link --overwrite python@2
