The if statement that was supposed to check if the Magento cache type was set to the string "varnish", actually set the cache type to "varnish".
This resulted in that the Varnish cache was always purged, when some other cache type was purged.
Merge pull request #19 from christofer-roth/patch-1

The if statement that was supposed to check if the Magento cache type...
Update README.md
Update README.md
Merged upstream