But that shouldn't matter in this case, "development" is the default environment, so this should work fine.
To debug it, make sure you're log level is set high enough, so you don't miss warnings and errors. You can use the logger() function in your code to write log entries, so you can later check the logs to see how it went.
All my tasks contain at least a 'start' and a 'stop' log entry, and I also log things like "xxx records processed" so I have an idea of what the task has done.
Have you checked your cron logs to see if it actually starts?
It is very likely that you don't have an environment in a cron call, which means no search paths, which means 'php' can not be found. I need to prefix it here with the full path to make it work.
use 'which php' to find the full path (probably something like /usr/bin/php).