🎨 add knexMigratorFilePath for knex-migrator initialisation (#7583)

no issue
- if we don't pass our root path, it can happen that knex-migrator get's the wrong path when looking for the .knex-migrator file

core/server/index.js

@@ -30,7 +30,9 @@ var debug = require('debug')('ghost:boot:init'),
     scheduling = require('./scheduling'),
     readDirectory = require('./utils/read-directory'),
     utils = require('./utils'),
-    knexMigrator = new KnexMigrator(),
+    knexMigrator = new KnexMigrator({
+        knexMigratorFilePath: config.get('paths:appRoot')
+    }),
     dbHash;
 
 function initDbHashAndFirstRun() {