Only clear task if it's already defined
Only clear task if it's already defined

Else rake throws a RuntimeError, "Don't know how to build task 'lint'"

keeleysam/puppet-lint,toby82/puppet-lint,rothsa/puppet-lint,danzilio/puppet-lint,raphink/puppet-lint,Rovanion/puppet-lint,rodjek/puppet-lint,paulgeringer/puppet-lint,yulis/puppet-lint