Regenerate gemspec for version 0.5.1

Regenerate gemspec for version 0.5.0

Regenerate gemspec for version 0.4.3

Regenerate gemspec for version 0.4.2

Regenerate gemspec for version 0.4.1

Regenerate gemspec for version 0.4.0

Regenerated gemspec for version 0.3.0

Regenerated gemspec for version 0.2.3

Regenerated gemspec for version 0.2.2

Fail purge if queue does not exist.