Fix a typo

tar_readings
tag_readings
  ^

en/_posts/2016-04-15-pgroonga-1.0.6.md

@@ -54,7 +54,7 @@ INSERT INTO tag_readings VALUES ('PGroonga', 'ピージールンガ');
 INSERT INTO tag_readings VALUES ('pglogical', 'ピージーロジカル');
 ```
 
-You need to create indexes against tag names and tag readings. It's important that `pgroonga.text_term_search_ops_v2` operator class is used for `tags.name` and `tar_readings.katakana`.
+You need to create indexes against tag names and tag readings. It's important that `pgroonga.text_term_search_ops_v2` operator class is used for `tags.name` and `tag_readings.katakana`.
 
 ```sql
 CREATE INDEX pgrn_tags_index ON tags