Update spatialdb.pp

It seems to be necessary to call the shell explicitly if you run shell commands. It was not the case in older versions of puppet and there seems to be a lot of discussion whether or not this should be the behaviour. Nevertheless, it works that way. The error I got prior that change was "Could not find command sudo" 

See among others:

https://groups.google.com/forum/#!topic/puppet-users/LWlzPpjKJOA

According to the forum entries it did not make it in the ChangeLogs. Unfortunately, I did not found any hints on that issue referring to Puppet 3.