Save migrations file on db (#215)

* Revert "Migration sql changes (#199)"

This reverts commit 12c834469c.

* Save migrate file on db

* Add message on migration error in lamassu-update

migrations/015-paired_devices.js

@@ -2,9 +2,9 @@ var db = require('./db')
 
 exports.up = function (next) {
   var sql = [
-    db.dropColumn('devices', 'authorized'),
-    db.dropColumn('devices', 'unpair'),
-    `CREATE TABLE IF NOT EXISTS paired_devices (
+    'alter table devices drop authorized',
+    'alter table devices drop unpair',
+    `create table paired_devices (
       device_id text PRIMARY KEY,
       created timestamptz NOT NULL default now()
     )`