bootstrap wrap migrations in once

Author: nekufa

README.md

@@ -10,7 +10,7 @@ Install using composer.
 ```json
 {
   "require": {
-    "tarantool/mapper": "2.2.0"
+    "tarantool/mapper": "^2.2.2"
   }
 }
 ```

src/Bootstrap.php

@@ -19,11 +19,14 @@ public function register($instance)
 
     public function migrate()
     {
+        $schema = $this->mapper->getSchema();
         foreach($this->migrations as $migration) {
             if(!is_object($migration)) {
                 $migration = new $migration;
             }
-            $migration->migrate($this->mapper);
+            $schema->once(get_class($migration), function() use ($migration) {
+                $migration->migrate($this->mapper);
+            });
         }
     }
 }