Correct grammar in parent field doc

docs/reference/mapping/fields/parent-field.asciidoc

@@ -103,7 +103,7 @@ GET my_index/_search
   cannot be established between documents of the same type.
 
 * The `_parent.type` setting can only point to a type that doesn't exist yet.
-  This means that a type cannot become a parent type after it is has been
+  This means that a type cannot become a parent type after it has been
   created.
 
 * Parent and child documents must be indexed on the same shard.  The `parent`