fixed sequence plugin typo

Author: nekufa

README.md

@@ -254,13 +254,13 @@ $mapper->get('shift_pattern', 1)->pattern[5]; // read element with index 5 from
 If you want you can use sequence plugin that generates next value based on sequence space.
 Or you can implement id generator using any other source, for example with raft protocol.
 ```php
-$post = $mapper->getSchema()->createSpace('post');
-$post->addProperty('id', 'unsigned');
-$post->addProperty('title', 'str');
-$post->addProperty('body', 'str');
-$post->addIndex('id');
+$mapper->getSchema()->createSpace('post')
+  ->addProperty('id', 'unsigned')
+  ->addProperty('title', 'str')
+  ->addProperty('body', 'str')
+  ->addIndex('id');
 
-$mappr->addPlugin(Tarantool\Mapper\Plugins\Sequence::class);
+$mapper->addPlugin(Tarantool\Mapper\Plugins\Sequence::class);
 
 $entity = $mapper->create('post', [
   'title' => 'Autoincrement implemented',