Fix duplication of modules during db update run

The tag work changed primary key of Dist table and this made
->update_or_create fail to update existing stuff, since we're not
passing it the primary key. So it dupes the modules during build,
and at the end of the build the originals get assumed to be old,
deleted dists and are tossed.

Fix by using meta URL as primary column.

Author: zoffixznet

lib/ModulesPerl6/Model/Dists/Schema/Result/Dist.pm

@@ -1,8 +1,7 @@
 package ModulesPerl6::Model::Dists::Schema::Result::Dist;
 use     ModulesPerl6::Model::ResultClass;
 
-primary_column dist_id       => { data_type => 'integer', auto_increment => 1};
-column         meta_url      => { data_type => 'text',                     };
+primary_column meta_url      => { data_type => 'text',                     };
 column         name          => { data_type => 'text'                      };
 column         author_id     => { data_type => 'text', is_foreign_key => 1 };
 column         build_id      => { data_type => 'text', is_foreign_key => 1 };