Parse the expiration time as an INT (#392)

* handle expire time as int

* Removed logging

* Update lib/document_stores/postgres.js

lib/document_stores/postgres.js

@@ -7,7 +7,7 @@ const {Pool} = require('pg');
 
 // A postgres document store
 var PostgresDocumentStore = function (options) {
-  this.expireJS = options.expire;
+  this.expireJS = parseInt(options.expire, 10);
 
   const connectionString = process.env.DATABASE_URL || options.connectionUrl;
   this.pool = new Pool({connectionString});