added counter to keys table

this lets us increment uses when a key is going to be used

server/migrations/2020-06-02-055256_keys/up.sql

@@ -5,5 +5,6 @@
 CREATE TABLE IF NOT EXISTS `keys`(
     `id` varchar(64) NOT NULL,
     `limit` integer,
+    `uses` integer, 
     PRIMARY KEY(`id`)
 );