fixed modulefile description error

Author: Tobias Martin

Modulefile.erb

@@ -4,7 +4,7 @@ source        '<%= metadata.source %>'
 author        '<%= metadata.author %>'
 license       '<%= metadata.license %>'
 summary       'This module installs and manages <%= metadata.name %>'
-description   '<%= metadata.description %>. Based on stdmod/puppet-skeleton-standard 0.0.5.'
+description   '<%= defined?(metadata.description) ? metadata.description : metadata.summary %>. Based on stdmod/puppet-skeleton-standard 0.0.5.'
 project_page  '<%= metadata.project_page %>'
 dependency    'puppetlabs/stdlib'
 dependency    'example42/stdmod'