add worker with analyze go.mod(pref ver util)

storage/migrations/postgres/000001_init_schema.up.sql

@@ -14,7 +14,8 @@ create table if not exists comment (
 create table if not exists module (
     id serial not null unique primary key ,
     name varchar not null ,
-    version varchar not null
+    version varchar not null ,
+    last_version varchar not null
 );
 
 create table if not exists issue (
@@ -34,4 +35,5 @@ create table if not exists package (
     comments integer[] default '{}'::integer[]
 );
 
+create unique index module_info on module(name, version);