Update packages.md

This is absolutely minor, but... with the leading slash it produces `/path/to/database//migrations` - with the unwanted additional slash.

packages.md

@@ -189,7 +189,7 @@ You may want to publish groups of package assets and resources separately. For i
         ], 'config');
 
         $this->publishes([
-            __DIR__.'/../database/migrations/' => database_path('/migrations')
+            __DIR__.'/../database/migrations/' => database_path('migrations')
         ], 'migrations');
     }